PHP/SQL Lookup - App Repair / Issue Resolution

We have an on-prem, small PHP webapp running on IIS (Server 2016) that looks up a telephone number and returns the result to our phone system. Our phone system routes incoming calls based on whether the CallerID number exists in a database, what type of company (client, vendor, unknown). When we migrated the application to Windows Server 2016, some functionality relating to the second database lookup stopped working. Here is the workflow: --> Incoming Call --> Phone system (Switchvox) passes the callerID to the app which then looks up the number in our CRM database. This is done on the Switchvox side using an event trigger - [login to view URL] --> If CallerID number is in the CRM database, the app sends the name of the caller, the type of caller (client, vendor, or unknown) back to the phone system along with the extension the call should be routed to. The phone system then handles the call from there. --> If CallerID number is not in the CRM database, the app then queries a second database which contains company name, first/last name, telephone number and contact type - client/vendor. The apps then sends the name of the caller, company, CallerID and what extension the call should be routed to. The phone system then handles the call from there. -->If the CallerID is not in either database, it then routes the call based on the area code of the incoming call. As previously mentioned, the second database lookup is not working. If we go to the event trigger URL manually, we get a 500 error.