For some reason, whenever I try to make a custom design, it gives me this alert saying, “ E1103: Insufficient storage space.”
What the heck is happening?

Storage space is not unlimited. It means that you used the default allocated storage per user. Go to the texture section in the part manager. If you follow the Mecabricks advice you can already store a couple of hundred custom parts.

Ok, thanks scrubs!

Hi, this same thing happened to me, but when I delete old custom parts it still shows the screen
I have created another account but it still shows the same issue