As a French native speaker, I'm a little bit surprised by the corrected text OP posted in her/his article ( http://www.runwes.com/images/learningfrench/image1.png ). Most of the corrections she/he received are not justified at all. Like using the work "crédits" is totally fine in this context. I can't get why they corrected some connectors like "à" or "pour", as the usage of these in the text seem at least as correct…
I'm also a native speaker (France's French if that makes a difference). "Crédits" was replaced by "bons", which means vouchers. In the context that would indeed be the likely correct option (and I never heard "crédits" used that way...) It's grammatically incorrect to write "s'inscrire à une salle de sport" and should indeed be "dans une salle de sport" and so it was warranted to correct that. The other corrections a…
I'm not even sure. If you consider a "salle de sport" is an activity rather than a place, it becomes correct. You would say "s'inscire à la piscine" (for swimming-pool) for instance because "piscine" is considered an activity rather than a place, in this context.