I am unfamiliar with digital illustrations as you describe it (no auto tracing, or reference image used), but in my mind it should work the same as a drawing on paper. Upload it as ‘illustration’ and add a digital property release.
However.. This is the info from the support centre :
Digital illustrations
If you made the image digitally, without any reference images, there is no need to provide any additional documentation with your submission.
Basically, I am reading this as ‘upload as ‘illustration’ without extra info. I assume that’s what you did, but resulted in the ‘mis