All our artwork specifications for each product are shown under the "Artwork Guide" at the bottom of the page of the product.
As long as it matches these it should be fine to use. We always ask customers to send over their artwork at 300dpi and the correct dimensions shown on the artwork guide. If you need help setting up your artwork, we do have Photoshop templates available for most of our products.
If you are still unsure, please feel free to email our Customer Experience team at firstname.lastname@example.org.