I got the same issue. I'm pretty sure that my client is qualified to claim $7,500 credit for his new Tesla Model Y, but like what you said, it was not computing even though I entered all the VIN details. I just followed your instructions to manually input the expected credit amount, it works. I don't think this Form-8936 is not ready as of now since on the one hand no red error box popped out, on the other hand, we have to manually input the credit amount based upon our own computation. There must be some coding errors behind the scene during the debug process.