Multipart.FilesSchema . If the filename contains non-ASCII characters, the key become empty. As I'm Korean, I've tried to upload any file named '강아지.png', the error message keep showing me path: ["files"], message: is missing. When I change the filename into 'puppy.png' (which has same meaning), it works well. <form /> tag. It encodes the Korean characters into the UTF-8 encoding.