I read long ago about a platform where one can advertise their comic in a pool of other comics and it shows up as ads at the top or bottom of other comics. I think it was called rainbow or something. Do you know what I'm talking about?
Never heard about rainbow but I'm using https://www.comicad.net for ads on my site - you can add their ads anywhere on your comic as long as your able to edit the site's html code (so either having your own website or posting to comicfury, don't know any other comic platform that lets you use custom html)
Yeah, I have to second Comicad. In terms of amount spent to subs gained, it's massively outperformed Instagram ads and similar for me.