Since that is a report from your actual Square account, is there a problem on your site with names, dates, amounts, etc?

I don't know of a problem with 1.5.6c and PHP 7.4. I'm also not sure if the bootstrap mod for One Page Checkout will work with 1.5.6c

First get Zen Cart showing and collecting the correct data, then make sure you are up to date with the Square Web Apps.