I had several issues with my VPAY since Revolut changed it’s payment processor.
Unfortunately, the only thing for me that worked out to solve the problem was to switch to a VISA Classic.
I also used family a moment to top-up my account from their VISA Classic by sending them money first from the account my VPAY was linked to and topping-up in their name with their consent.
Maybe my last paragraph can temporarily solve your problem before changing your main card.
PS: What I mentioned before was on an account with money on it. Revolut is indeed checking the balance of your VPAY as a VPAY require a systematic authorization before paying. So with no money on your VPAY card means no authorization and so failed addition of the card to Revolut.