When sending by URL the target file must have the correct MIME type (e.g., audio/mpeg for send Audio, etc.). In send Document, sending by URL will currently only work for gif, pdf and zip files. To use send Voice, the file must have the type audio/ogg and be no more than 1MB in size. 1–20MB voice notes will be sent as files. Other configurations may work but we can't guarantee that they will.