Hi @legend,
The submission limit is calculated based on a rolling window going backwards in time from today at 00:00 UTC. The message tells you that you had two previous submissions within that window. Once the older of those two submissions is more than 7 days ago, then you will regain another available submission.
You can see a more detailed explanation of how it works from this older post from a previous competition. Note that the other competition had a different number of submissions and a different period, but the mechanics work similarly.