"Sorry we could not fetch the image" Pinterest error even though Image is publicly accessible

Question

I am not sure what the real issue is but my image is publicly accessible via a url similar to

https://storage.googleapis.com/myapp.appspot.com/IMAGES/ead253addf86583ba57b7265ad9c999ba437b9ded695ac4b5bce6d78ccfe0c1b.png?GoogleAccessId=firebase-adminsdk-pgu3n%myapp.iam.gserviceaccount.com&Expires=253376550000&Signature=JgJcZK4vhn3uKThzcouTx7Pm92LrXhHEjxfPbvbiFzCXyUKH%2FuXhsH1M4Jn8KpUgi8HJcHqBMk2E7VEvHqEmmWLYmeGhBaDakZUSLQVUFEqbbxxU0e5RvsKOz66%2BymVywII9rL02xkjy10Is6ZibkfnSTG2xkNQ5XCdLoctSowZtu7dKf6OvZN48xI3cAPwcQbHLZ3n12I3%2BCsVnDiUcq4mybzKmA9e8dyKPvjYOskhmc0hO3bb%2BokxWF8wsyZ%2BGn7sjCgrvnyow%2FpxWm%2BlLVtEsbOFDZRUgmWOzgHNgcriX5MCLDNSmwRuRVl4xZtU0tcnX7dDp7XDiQqxU%2BBj6hQ%3D%3D

However whenever I submit the image url to pinterest api via the following request body:

 requestBody['media_source'] = {
                source_type: 'image_url',
                url: mediaUrl
 }

I keep getting back the following error message:

{
  "code": 1,
  "message": "Sorry we could not fetch the image."
}

But the url is very much accessible by anyone so why is pinterest unable to get this image.

It's really weird.

Please help.