What device are you using? Apps and phones sometimes throw up glitches. If using switch to a laptop/ PC / browser, see if that may help.
Or if paying with Paypal funds, do you have enough money in your Paypal account?
Paying with a card? Are those cards still in date?
If none of the above , I would call Paypal, they are very helpful up there in Paypal Towers, maybe they can solve the problem for you.
