Are the emails the same when you log into your online avast account and when you look on avast UI. menu>my subscriptions.
Ive been with avast for around 15 years. back then i used a totally different email address to register which no longer exists so my subscriptions are only showing for the last 2 years with my new email address.
If you are trying to renew with a different email then they wont connect so you cant pay so that could be why its greyed out.
another thing ive seen a few times on here were the card had expired so paypal had not updated with new card details so just hangs.
just guesses though while you wait for others to advise.