On the Vistaprint website it says that PSD format is recommended, but it won't allow me to select my PSD file. It says CS3 Image. I'm currently using PS CC 2019.
"We support a variety of file formats for uploaded designs. Adobe Acrobat 9 Document (.pdf) (recommended) Adobe Illustrator CS3 Artwork (.ai) (recommended) Adobe Photoshop CS3 Image (.psd) (recommended) Bitmap Image (.bmp) GIF Image (.gif) JPEG Image (.jpg,.jpeg) Microsoft PowerPoint 2010 Document (.ppt) Microsoft Word 2010 Document (.doc) PCX Image (.pcx) PICT Image (.pic,.pict,.pct) PNG Image (.png) PostScript Document (.ps) TIFF Image (.tif,*.tiff)"