If I am correct, the client checks the first part of the key, then connects to the auth server for the rest of the key.
Which is why it says full version unlocked, then auth fails.
The client checks whether the key tail is a possible combination of letters (there are
many possible combinations), and the auth server knows which combination belongs to the id (first 5 letters).
So if you get a letter wrong or two, it might still be a possible combination, so you first see 'full version unlocked', then it starts authenticating and the server tells you the key is invalid.
Make sure you copy+paste the entire key so there are no spelling mistakes.