Supabase Storage errorSupabase Storage: upload rejected for its MIME type

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Why the file type is rejected, and the fix

1. 01

   The bucket doesn’t allow that type

   A bucket created with allowedMimeTypes rejects types outside the list. iPhones save HEIC photos, and many tools export WebP, so a JPEG and PNG list misses them. Edit the list in the dashboard under the bucket’s settings.

2. 02

   The upload sends the wrong content type

   “By default, Storage will assume the content type of an asset from the file extension.” Supabase docs, Standard uploads (Content type)

   Without a file extension, Storage can’t infer the type. Pass the real type with the upload, and stop if the browser reports none.

   if (!file.type) throw new Error('Unknown file type');
   await supabase.storage.from('avatars').upload(path, file, {
     contentType: file.type,
   });

3. 03

   The contentType value is malformed

   “The specified MIME type is not valid.” Supabase docs, Storage error codes (InvalidMimeType)

   A value like jpg or image instead of image/jpeg isn’t a MIME type. Send the full type and subtype.

4. 04

   The rule is right and the file is wrong

   If the bucket should only take images, keep the rule. Check the type in the browser before upload and show the user which formats work.

Checked against the vendor’s docs on November 9, 2026: Supabase docs: Storage error codes; Supabase docs: Creating buckets; Supabase docs: Standard uploads.

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