Hi Indresh,
So if I go through the process of adding something to basket, going to cart (also reindexing doesn't fix the issue with the popup saying go to cart leading you to a 404 but that's another issue) then going through and entering details for postage etc.
The final stage where you have the option of paypal or stripe. If you click stripe then proceed to pay, it then errors out like attached.
I checked and the OAuth works fine for the Standard account we have, so the sellers account seems to be registered correctly to the payment system, but it is when I go to pay that this occurs.
Cheers
Sam