There can be many reasons for this -
You have consumed all your credits.
If you purchased one-time additional credits, they expire at the end of billing month
If you are a new user - and you skipped work email verification during signup, then you do not get any free credits. We provide free credits for trial when you signup using work email address and verify it.
If you are a new user - and if you used temporary or fake email for signup, you do not get any free credits
If multiple accounts are created from same IP within a short span, such accounts are flagged, and if any abuse is detected then no free credits are given