Here are a few of things you could try:
-- check that you're using the correct fingerprint for the version of
your app - i.e. release vs debug
-- check that you're specifying both the fingerprint and package name
with the correct capitalization (they are case sensitive)
-- check that you've not accidentally putting any spaces or other
characters into either field (e.g. due to copying and pasting from
google)
If none of that works, please email us at
he...@thrutu.com with the
full details of your app and we will help you to get an API key
working.