I wanted to create a new code space for some work, but when I try to I get this error:
You're at 100% of your included usage for this billing period. For more information, view your billing settings.
The thing that I don't understand is that I don't have any code space. Did some searching and I found that 19.95Gb were only the prebuilt. I removed some of my repositories that showed the storage of the prebuilds, but I still get this error.
GitHub has some documentation on this. There's a storage limit you can control, and the limit is in GB-month. For example, 1 GB-month is equivalent to storing 1 GB for the entire month, or 2 GB for half a month, and so on. There's also a number of hours of usage per month that's included.
Once you've exhausted that, it doesn't return until the beginning of the next billing period. Simply deleting the storage will free the data and it won't be used next month, but it won't make you able to create a Codespace now since you've exhausted the storage limit.
If you want to create a Codespace nevertheless, you can increase the billing limit by putting down a credit card and specifying how much you're willing to spend, and then the usage will be allowed up until you hit the limit.