Can't Insert Video Record Into The Database

I have just installed ClipBucket V4.2 RC1. I have Centos 7 and the latest version of all the tools including PHP 7.3. In fact all requirements specified. My Hosting Provider has checked that everything is present.

But when attempting to upload a video it will show the progress bar which will complete and turn green once it hits 100%, but the inserted progress bar above that doesn’t show any progress and stays at inserted 0 of 0, which means that no record has been inserted into the database and therefore the “Submit Now” button at the bottom won’t work.

So no database record is being created and using the browser console to try and find out more I see the following errors reported:

POST actions/file_uploader.php
[HTTP/1.1 500 Internal Server Error 13025ms]

Failed to load resource: the server responded with a status of 500 (Internal Server Error)
actions/file_uploader.php:1

So of course my question is what is preventing the database record being created? Obviously the immediate cause is file_uploader.php not loading, but why is this?

We’re told to use PHP 7.3 but is this definitely correct? I have 7.3.25.

If this is correct I cannot think in what way my server is lacking?