In late November I upgraded a client who has been using NopCommerce for 2 years solid with PayPal. They haven't had one issue with PayPal, it just worked. After I upgraded I installed the exact same PayPal account and it worked fine for about 2 weeks. I witnessed orders processing and even purchased a 10 cent test item from their account to make sure. Then in december their customers started seeing the following message.
There's a problem with the merchant's PayPal account. Please try again later.
This is the only error message I see... nothing in the logs as it's on PayPals end.
So I tried purchasing an item and got the same error. I had my client contact PayPal and they were told that their account is fine.
What are some reasonable troubleshooting steps for me?
note: I'm hosting on Azure if that matters