Thanks for your response! I was suspecting the same thing, so I installed PHP 5.6 & 7.0 and changed my virtual host PHP configuration to try the older versions but still get the same 500 internal server error. The apache error log shows this message when I request a page:
[Fri May 26 17:35:11.881460 2017] [core:error] [pid 19156] [client 181.167.162.169:44968] AH00124: Request exceeded the limit of 10 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace., referer: http://www.transactioncart.com/setup/
So I changed the LogLevel to debug and here is my error log output now:
[Fri May 26 17:46:33.131545 2017] [ssl:debug] [pid 19146] ssl_engine_pphrase.c(181): AH02199: SSL not enabled on vhost transactioncart.com:80, skipping SSL setup
[Fri May 26 17:46:38.226069 2017] [authz_core:debug] [pid 20085] mod_authz_core.c(809): [client 181.167.162.169:45298] AH01626: authorization result of Require all granted: granted
[Fri May 26 17:46:38.226165 2017] [authz_core:debug] [pid 20085] mod_authz_core.c(809): [client 181.167.162.169:45298] AH01626: authorization result of <RequireAny>: granted
[Fri May 26 17:46:38.226271 2017] [authz_core:debug] [pid 20085] mod_authz_core.c(809): [client 181.167.162.169:45298] AH01626: authorization result of Require all granted: granted
[Fri May 26 17:46:38.226288 2017] [authz_core:debug] [pid 20085] mod_authz_core.c(809): [client 181.167.162.169:45298] AH01626: authorization result of <RequireAny>: granted
[Fri May 26 17:46:41.173356 2017] [authz_core:debug] [pid 20084] mod_authz_core.c(809): [client 181.167.162.169:45310] AH01626: authorization result of Require all granted: granted
[Fri May 26 17:46:41.173406 2017] [authz_core:debug] [pid 20084] mod_authz_core.c(809): [client 181.167.162.169:45310] AH01626: authorization result of <RequireAny>: granted
[Fri May 26 17:46:41.173497 2017] [authz_core:debug] [pid 20084] mod_authz_core.c(809): [client 181.167.162.169:45310] AH01626: authorization result of Require all granted: granted
[Fri May 26 17:46:41.173512 2017] [authz_core:debug] [pid 20084] mod_authz_core.c(809): [client 181.167.162.169:45310] AH01626: authorization result of <RequireAny>: granted
[Fri May 26 17:46:41.505283 2017] [authz_core:debug] [pid 20084] mod_authz_core.c(809): [client 181.167.162.169:45310] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.505299 2017] [authz_core:debug] [pid 20084] mod_authz_core.c(809): [client 181.167.162.169:45310] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.541089 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.541182 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.546789 2017] [authz_core:debug] [pid 20085] mod_authz_core.c(809): [client 181.167.162.169:45312] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.546807 2017] [authz_core:debug] [pid 20085] mod_authz_core.c(809): [client 181.167.162.169:45312] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.560439 2017] [authz_core:debug] [pid 20087] mod_authz_core.c(809): [client 181.167.162.169:45316] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.560477 2017] [authz_core:debug] [pid 20087] mod_authz_core.c(809): [client 181.167.162.169:45316] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.854052 2017] [authz_core:debug] [pid 20084] mod_authz_core.c(809): [client 181.167.162.169:45310] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.854067 2017] [authz_core:debug] [pid 20084] mod_authz_core.c(809): [client 181.167.162.169:45310] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:41.879912 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/views/assets/fonts.css
[Fri May 26 17:46:41.879931 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/views/assets/fonts.css
[Fri May 26 17:46:44.033449 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.033471 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.033539 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.033556 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.193434 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.193455 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.193607 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.193618 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.193739 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.193749 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.193861 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.193871 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194012 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194024 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194231 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194248 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194390 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194400 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194537 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194547 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194693 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194703 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194854 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.194864 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195045 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of Require all granted: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195056 2017] [authz_core:debug] [pid 20086] mod_authz_core.c(809): [client 181.167.162.169:45314] AH01626: authorization result of <RequireAny>: granted, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195157 2017] [core:error] [pid 20086] [client 181.167.162.169:45314] AH00124: Request exceeded the limit of 10 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace., referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195180 2017] [core:debug] [pid 20086] core.c(3531): [client 181.167.162.169:45314] AH00121: r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195185 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195189 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195193 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195197 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195201 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195205 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195217 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195222 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195226 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /home/transactioncart/public_html/setup/index.php, referer: http://www.transactioncart.com/setup/
[Fri May 26 17:46:44.195230 2017] [core:debug] [pid 20086] core.c(3538): [client 181.167.162.169:45314] AH00122: redirected from r->uri = /setup/requirements, referer: http://www.transactioncart.com/setup/
adding the LimitInternalRecursion 100 directive didn't help either...