Is there an ELI5 for this? I really don’t understand what was under a quota and what it means that the quota had a grace period. Did YouTube not update their a

Is there an ELI5 for this? I really don’t understand what was under a quota and what it means that the quota had a grace period. Did YouTube not update their authentication to a new version of the api, but they had a quota for old api calls that ran out?