I tried training on the minimum number of samples instead of my full dataset and when I did that I got this error message in validation:The job failed due to an invalid training file. Invalid file format. Line 1, key "messages": The last message must be from the assistant
So I just added an assistant message as the end message to all my samples and it now seems to be training.
Weird since it passed validation with my full dataset, but showed the message when it was just a subset. Anyways, that seemed to do it.