I have tried other sites like Society6 and Redbubble without having any uploading issues while Society6 has 150 Mb file size limit while Redbubble has 300 Mb. I do not know why Merch 25 Mb only because it is impossible for my artworks to meet the guidelines without exceeding 25 Mb. I always getting "Upload error. Please check design guidelines and try again." because of file size and when trying to change the resolution to reduce the size i get the same error. Any help?