@adan84: i did some research for this extensions, there's a news since 2019 says that Avast were tracking a user's activity as they are browsed the web. and because the extensions marks dangerous links in search results and stops users from visiting phishing sites. i don't think its good anymore because of how annoying it is to reach sites you wanted to but being block.

And the reason that you cannot make the payment for the extension, i did some research again.. and i found another news sites saying Avast stops selling its antivirus and CCleaner software in Russia because of Russia's invasion of Ukraine. so the company officially suspended all marketing and sales to Russia.
Ref.
The News since 2019
https://www.bleepingcomputer.com/news/software/avast-and-avg-firefox-extensions-pulled-from-mozilla-addons-site/

Selling suspended
https://mind.ua/en/news/20268921-czech-avast-stops-selling-its-antivirus-and-ccleaner-software-in-russia

looks like you gotta quit this one and use other software man 🥲
I look up on youtube and they recommend these VPN that works by hiding your VIP and prevent you from be taken data through sites or public connection
NordVPN, Proton VPN, idk, you can look up on internet for something suit you, good luck 🫡