If you are having difficulty creating clothing, there are a few things to look into.
All images that are uploaded will need to be either a .gif, .png, or .jpg file.
Make sure your image is the correct size. It is always important to use the appropriate template when creating your clothing, but occasionally the size of the image can shift by a pixel or two when editing or saving. If this happens it can give you an error telling you to be sure to use a template even if you already did. If this happens, ensure that your image is the correct size and try uploading again.
Note: Creators are required to pay a Marketplace fee to create shirts and pants or to sell t-shirts.