UploadSiteHostedPictures API call returning the error "ExternalPictureURL server not available"

Summary 

When executing the UploadSiteHostedPictures API call for the ExternalPictureURL, call is returning the below error: 

<ShortMessage>ExternalPictureURL server not available</ShortMessage>
<LongMessage>The server specified by ExternalPictureURL is not responding</LongMessage>
<ErrorCode>21916543</ErrorCode>

While the ExternalPictureURL can be accessed through browser, Postman or any other application.

Detailed Description

There can be several reasons for the error 21916543, one of the reasons can be that the picture URL domain has duplicate certificates. According to TLS1.2 RFC https://www.rfc-editor.org/rfc/rfc5246#section-7.4.2, duplicated cert is not allowed.

In the real world some clients may tolerate it, but it may cause odd issues on the other clients so the UploadSiteHostedPictures call is returning the error "ExternalPictureURL server not available for the URL" while URL can be accessed through browser, Postman or any other application.

You can check for the picture URL domain and fix the issue for the duplicate cert to avoid the error 21916543 for the call.