The fact that PayPal is looping tells me something's wrong with your browser. I've seen PayPal do that infinite loop when one of its cookies gets stuck of a browser extension is blocking its JavaScript.
Moreover, it's possible that a browser extension does block JavaScript which is why the credit card payment would fail too.
Please try using a different browser, without any browser extensions installed. If you're on Windows I recommend portable Firefox. If you're on Linux or macOS try installing a browser you're not already using such as Brave or Opera. The payment should now work just fine.
Nicholas K. Dionysopoulos
Lead Developer and Director
🇬🇷Greek: native 🇬🇧English: excellent 🇫🇷French: basic • 🕐 My time zone is Europe / Athens
Please keep in mind my timezone and cultural differences when reading my replies. Thank you!