What is the correct format of the image URL while sending a POST request to an endpoint e.g. talks?

Hi,

I am using the following URL (I used a Dummy URL but the format is the same as this) to POST a request to the talks endpoint:

It's a png type image and it's public. However, whenever I send a request, I receive the following error:

textPayload: " description: 'Could not process your image, Please check the image is public and in a supported mime type - image/jpeg or image/png'"

Do I, by any chance, have to have a URL that ends with the file type? If this is the case, it limits the scope of work, no?

I hope to hear from you soon.

Regards,
Ray