Thanks for posting a question here in the Community, @vincenzo.
The fees or pricing for the online bill pay depends on the type of plan you have. Please check out this article to learn more about the fees per plan type: What are the fees per plan type for the Online bill pay subscription?
I'm also thinking of adding these handy articles that you can read through to learn more about Online bill pay in QuickBooks Online:
Fill me in if you have more questions by leaving a comment below. I'm around in the Community to help you achieve your goals. Take care and have a nice day!