Upload the file with the highest quality you have, up to 64 MB.
Only uploading PDF files (* .pdf) is allowed, if your file is not of this format it will be rejected.
The fonts or texts must be converted into paths or curves, also check your design correctly to avoid misspellings.
Try not to use masks and transparencies or flatten them.
It is mandatory that your file, spot colors and Pantones are correctly converted to CMYK to avoid large variations in color.