Not all problems or issues in web development can be detected during development or testing. There are even web application errors that are hard to catch like runtime errors.
PHP version compatibility issues:
1. Login to Cpanel
2. In software Section click on "MultiPHP Manager".
3. Select a domain for which you want to change PHP version.
4. Select PHP version from a dropdown.
Check Error-Log:
1. Login to Cpanel.
2. In Files Section click on "File Manager".
3. Click on public_html or write "www" in a search bar.
4. You will be able to view an error_log file in this directory.
5. Right click on an error_log file and click on "View".
6. The PHP log messages provide you with the file and line number of the error, notice or warning. That information will be very useful to find the source of the problem.