If an error theory beleives that all morals try to describe objective moral judments that do not exist, then how can moral claims be truth apt if all morals are an error?

I've really tried my hardest to understand, but it seems too contradictory to me. I'm just in the beginning of studying metaethics. I'm sorry; I don't think I'm smart enough for this. How can someone believe every moral claim tries to state something that doesn't exist WHILE still being categorized as a cognitivist, which says things can be evaluated as true or false? If a moral judgement can be evaluated as true or false relative to the framework being used, then how can an error theorist even evaluate it in the first place if the framework being used is that all morals are an error?

Edit: Okay, it seems I can't reply to comments due to not being a panelist. Confused, but gonna summarize what I think. So because there is a chance it could be true (which why is there even a chance, since all morals are describing something not there, so it's an error automatically?), though it's not to an error theorist, there is the possibility of there being an answer to something. This is truth apt. But a moral error theorist believes the answer to the possibility of it being true as false since the truth apt is a description and the theorist believes it's describing something that isn't there?

Edit 2: Still can't reply. Says I must be a panelist. Since I don't have a flair, I must get from a mod. But thank you all so much cause I'm kinda understanding it better!