I believe its a fair assumption that if you set a budget, the request would start to fail -> rejected once you hit said limit.
However, this does not seem to be the case as my budget was reached and requests were still being sent resulting on all my leftover credits being drained.
Its not a big deal as there were only 15$ credits left. However, the damage could have been a lot worse.
Is this the expected behavior? Was I being naive to expect it to be a hard limit?