Can't activate avast clean up

Hello,
I renewed my clean-up subscription but it’s impossible to insert the activation code. When I try, a message pops up, saying: “impossible to elaborate your request in this moment. Try again [574]”, but it seems it’s never the right moment. More, I tried other buttons (as “activate”) and it asked me my account password. After logging into my account, the window started saying only “error”.

How can I solve this situation and make Clean up run?

Please (re)search before posting (read threads).
This issue is well known and handled in many other threads already.