I guess the worst case scenario is that i have to return the adapter and have to buy another disc brake.
Might be a idea to ask the seller about returns, that adapter is anodised red and attaching it to a fork with a brake might take some of the red anodised colour off the adapter which would make it look like a used adapter.
If I took a picture of the bike brake, would it help you give me more concrete evidence or not?
Possibly, it wouldn't hurt.
Are all Post mount sizes the same
As far as I know all PM brakes use the same size mount.