HELP!! I need the List of external API's accessed by suiteCRM???

I’ve been trying to figure out what is going on with not being able to add invitees to Meetings and my only thought is that there is something being blocked by my server.
Here’s why–
I’ve tried all the fixes listed in various posts.
I’ve tried php 5.6.2
I’ve tried the newest version of SuiteCRM to see that would work.
(current production version in use is 7.3.1)
All works fine on my dev server same version of IIS and php and mysql
I load the same files and database to the production server and I get an “Invalid Character” error unless I remove any “Group Only” settings in the Security Suite Module.

Please help.