Supabase Storage errorSupabase Storage: “The resource already exists” on upload

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Why the upload collides, and the fix

1. 01

   Every upload uses the same file name

   “When uploading a file to a path that already exists, the default behavior is to return a 400 Asset Already Exists error.” Supabase docs, Standard uploads (overwriting files)

   Names like avatar.png or the original file name collide on the second upload. Put a unique part in the path.

   const path = `${user.id}/${crypto.randomUUID()}.png`;
   const { data, error } = await supabase.storage
     .from('avatars')
     .upload(path, file);

2. 02

   The app means to replace the file

   “Use x-upsert:true header to overwrite the resource.” Supabase docs, Storage error codes (ResourceAlreadyExists)

   For a profile photo that should overwrite the old one, pass upsert: true in the upload options.

   await supabase.storage
     .from('avatars')
     .upload(`${user.id}/avatar.png`, file, { upsert: true });

3. 03

   upsert is on, but the policies only allow INSERT

   “To allow overwriting files using the upsert functionality you will need to additionally grant SELECT and UPDATE permissions.” Supabase docs, Storage access control

   Overwriting reads and updates the existing row in storage.objects, so an INSERT-only policy is not enough. Add SELECT and UPDATE policies with the same folder check.

4. 04

   Users still see the old file

   “Uploading a file to a new path is the recommended way to avoid propagation delays and stale content.” Supabase docs, Standard uploads

   Also check: an overwritten file can stay cached at the edge for a while. A new path per version avoids stale images.

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

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