Errors with Paypal Standard using sandbox account

Hello,

A client of ours reported strange bugs while testing our Real One Page Checkout plugin with Paypal Standart. Sometimes during checkout, while getting redirected to the PayPal page to enter a credit/debit card, they would get a 500 Internal Server Error from the Paypal site.

We started investigating this issue with our plugin. We tested for 2 days straight and got nowhere since about 50% of the requests will lead to an error on the Paypal's side. The situation got even more strange because the same request (same products, user, addresses etc)  would firstly pass with no problem and on the second or third try would result in an internal error on the Paypal's site.

Then we decided to test if this issue is only present in our plugin, so we disabled it and started testing with a clean install of nopCommerce. We got the same results. About 50% of the requests to the Paypal site would result in an internal error on the Paypal's side.
As far as we can tell there is no difference between the request that pass and the requests that lead to an error.
We are really baffled by this situation and have no explanation to why these errors are happening.

It is important to note that we have never experienced this issue with normal Paypal account. So it looks like the problem is present only with the sandbox account.

Has anyone that have used Paypal Standard with Paypal sandbox account had any similar problems? Any information on this issue will be helpful!

Note: We tested using nopCommerce 3.9 with no customizations.

Regards,
Anton

Hi Anton,

Is it possible to share the string (URL) you post to PayPal when redirecting?

fyi, if you Google that error, others have experienced it:
www.google.com/search?q=500+Errors+with+Paypal+Standard+using+sandbox+account