Questions regarding additional payment features

Dear support

I plan to offer additional options (e.g. publishing an entry on Facebook) in addition to all listings (cost-based and free listings). Example: Someone enters a free entry. If he clicks on an appropriate link or something similar, he can choose (for an amount to be defined) that his contribution is also published on Facebook (this process will be done by me manually).

Is the implementation of such additional options somehow possible? I think it would have to be done in a different way than via the payment manager, since such options are to be offered additionally to all selected variants. It would be great if the invoice processing could also be handled automatically. Similar requests have certainly already been made by other users, right?

Thank you for your much appreciated support and feedback.

Regards
Jorge