Could be related to: 

Usually a new sandbox account fixes it.

@ryan I m testing in UnityEditor with iOS platform. Is this API works in Editor ? or we need to build on mobile to test ?

I’d always recommend building on a physical device for testing, there are a lot of quirks with the simulators and in-app purchases so testing on a physical device is a good way to rule that out while debugging. 

Ryan correct me if I am wrong, but I think you did not answer the original question.

Does your SDK/API work inside Unity Editor?

Because I can not list my products or offerings in Editor.

If it is the case please mention this in the documentation because I have lost a lot of time debugging and double checking my code.

10 days and no anwers? BUMP @ryan