You could also try uploading the file to Google Drive and sharing the link, which definitely works. If this is the case, try to attach the file to a separate thread and provide the link in your response instead. Larger worlds could exceed the file size limitations for posting a response.
Don't worry, this process doesn't harm the file or the world. Click on the file once and do CRTL-C to copy it.
If you're on a PC, type %USERPROFILE%\Documents\My Games\Terraria\Worlds into your file explorer's search bar.
