Can you please tell me why this is disabled? What limit is reached?

I just received an email saying...

Dear lombardosproperties, 

You have currently reached the limits of your account. Your forms are disabled now

Can you please tell me why this is disabled?  What limit is reached?

I did check your account and found that it is over quota as you have received payment submission limit. Please note that free account has only one payment submission limit. Since you have already received 1 payment submission that is the reason why your account is over quota.

To enable your form again, you will have to upgrade your account or wait for the first day of next month when the submission counters are reset.