Sorry for in Japanese, but this is the the screen shot for reason why it is rejected. I believe the reason is the first one, which raster element in the vector file. Does the Rainbow Gradient color is raster picture??
PNG file type should be used only for images with a transparent background. Though I assume it's an artistic choice, perhaps the missing and incomplete lines were a reason for rejection.
Thak you for your reply. I have uploaded different version which has only black line, and it has been accepted. I made both files outlined and no open paths, and both are submitted by AI. I used the rainbow dradient color for this line from the swatch panel >Gradient>Color combination. It must be something wrong with the selection....