If admin, then simple form with a PayPal payment works OK.
If not admin, form completes, but fails to trigger PayPal.
Looking at the saved entry and the debug logs, it’s as if most of the field data is not being saved. (Without this data, I would expect PayPal to fail.)
I have double checked everywhere for any permission restrictions - everything seems available.
Issues like the one you’re reporting are often caused by caching, it can be a plugin or a server side cache. In the same way people nowadays fully understand that caching an e-commerce cart or checkout page is not a good idea, the same applies to a GF form used for payments.
So if your site is using any kind of caching, I would recommend you to start the troubleshooting by turning it off. Then empty your browser cache, reload the page, and try again the form.