Hi, I'm getting the same issue.
I Install the pdo_odbc for PHP7.3 and also followed this instruction
The problem is I'm also getting the "503 Service Unavailable "

From my other client server which I also tried to setup this one, it works fine. But for the newly setup server I'm getting that issue. Also, take note the MSSQL server URL/IP has no restriction so I'm sure why it has issue on this new setup server.
Also, There are no log issue that has been added to error_log when I check all error logs in WHM CPanel and via terminal.
My setup is in Centos7.7 and CPanel v84.0.21
Thanks,
I Install the pdo_odbc for PHP7.3 and also followed this instruction
The problem is I'm also getting the "503 Service Unavailable "

From my other client server which I also tried to setup this one, it works fine. But for the newly setup server I'm getting that issue. Also, take note the MSSQL server URL/IP has no restriction so I'm sure why it has issue on this new setup server.
Also, There are no log issue that has been added to error_log when I check all error logs in WHM CPanel and via terminal.
My setup is in Centos7.7 and CPanel v84.0.21
Thanks,