What does it mean if i'm out of space?

The limit you have reached on your FREE ACCOUNT is the PAYMENT SUBMISSION LIMIT per month. Here's the complete denomination per plan for your reference:

FREE - 1 Payment Submission per month

BRONZE- 10 Payment Submission per month

SILVER - 100 Payment Submissions per month

GOLD - Unlimited Payment Submissions

Your forms will be disabled once you reach any of the monthly limits. And your options are:

1. To either wait for the limit to reset on the 1st day of the next month (this replenishes on a monthly basis)

2. Or upgrade to a higher plan that offers more payment submissions per month

These and MORE were discussed in great detail on the article I'm linking below.

Complete guide: Understanding-Your-Account-Usage-and-Limits