Strictly follow these requirements
Max print width: 22.8 in
* Design out of this area will be cropped/trimmed length
TIFF or PNG only with Transparent Background
300dpi is recommended
A transparent or translucent gradient IS NOT recommended; it will lose its “blending” effect where transparency of 30-40% will start to break and create jaggy edges in your artwork.
The Max print width is 22.8 inches. Any design that is out of this area will be cropped/trimmed.
Check your artwork’s edge quality and make sure they are sharp enough and does NOT contain “dirty” colors resulting from a badly removed background process.
Make sure you own the copyrights to print.