I remember there was some Bitcoin add-ons 5 years ago but they used websites api made by corporations. So the crypto went through their websites.
The problem with using add-ons that are made by corporations such as coinbase, bitpay, coinpayments is that they have TOS and if you break those TOS they will ban you. It's no different that paypal or stripe. Crypto is about bypassing these companies.
Use the software BTCPAY server. It's open source, installed & controlled by you so there is no TOS. It completely bypasses the traditional crypto payment processors. You are in control of your own crypto.
The BTCPAY Server team has a xenforo add-on.
Contribute to btcpayserver/xenforo development by creating an account on GitHub.
github.com
The only issue with BTCPAY Server you need to install the BTCPAY Server software and is it is not for beginners.
I installed it. It wasn't so hard but requires linux CLI knowledge. You could always use someone else's BTCPAY Server but i would install your own so you are in control of everything.
BTCPAY Server is just for crypto not traditional money. It's the future. Stripe & paypal will eventually go byebye