I noticed a similar post from a user earlier today about Paypal redirection issues, however, I do not have a service associated with my resource, and I think there may be a larger issue.

What seems to be happening is when a user clicks on the pay button to complete their appointment, they are directed to paypal, however, not to a payment screen, but to Paypal's homepage, I have a feeling this has something to do with the Paypal Production URL. Possibly Paypal has changed something in their systems which has affected this?

Additionally, people were making Payments as recently as Friday with my existing settings, thanks.

Not sure what to suggest there.
I just ran some tests from 3 different sites on different hosts and all connected to PayPal just fine.

I had a quick look on the PayPal Dev site forum to see if anyone was reporting connection issues but I could see none.

Is this Europe or North America? I can only test North America from here.

I am in the United States, the Paypal Production URL I'm using is: www.paypal.com/us/cgi-bin/webscr

I did have one thought, have you heard of Paypal banning a server IP because someone has made too many unsuccessful payment attempts? I know they temporarily disable your login if you make too many attempts.

I believe it can happen but I suspect it is very rare.

I have also heard of hosts disallowing redirects to another server. And/or blocking query string parameters.

The link should be and SSL like..
https://www.paypal.com/us/cgi-bin/webscr

Has anything else changed on your booking screen? Are you sending tokenized data to PayPal (ie: using ABPro's token system to include booking screen data in the PayPal payment screen).

Thanks for the response, I did have https:// in front of the URL, I will email my host and see what kind of response I get.

I haven't changed anything from Friday when it was working fine, and I have no tokens, the whole thing is a bit odd, thanks again!

As a follow-up, I went to the site this morning to do some additional testing, and everything worked fine, which is good. I have a feeling this issue had something to do either with Paypal or like the Admin mentioned above my server. If anyone runs into this in the future I would recommend contacting your server. Hope this helps.