When I submit a REST POST request to update an email content section endpoint which has the external url property, the request fails with this error: Marketo API error (701): "invalid url". It only gives me that error on certain websites, most of the website works.
Not working: (https://via.placeholder.com/1280x640.jpg).
I tried several different websites and most of them work, but some fail with that 701 error.
Is there some kind of validation in the url property that is not documented or that I am not aware of?