SAM claims I don't own a game ... but I do and here is proof! about steamachievementmanager

[P3rf3ctXZer0]

I used a super save back in the day but now I cannot undo my sin. I have all the DLC and if you aren't familiar with Afterbirth + basically its a mod tool for Issac Afterbirth that was also DLC. Anyways when it was first released you could not make progress in the game while using mod even if the mods were cosmetic only and now I am unable to legitly regain the achievements ... and it saddens me. I only used the save so I could enjoy everything after birth plus had to offer :( after some of my pushing the devs fixed it so basically as long as you beat mom once you can use mods while playing and make progress.

[gibbed]

It's not so much about proof, is that the Steam API that SAM uses says you don't own the game, and thus, cannot interact with it via the API.

[P3rf3ctXZer0]

Well I do I got it the day I came out I play daily so wtf.

[iBreakEverything]

I think you try to open a game with the wrong appID in SAM, but that is unlikely.
Anyway try 250900 or 250902
https://steamdb.info/app/250900/