Error setting up new Amazon Attribution Campaign

Hi I'm setting up a new Amazon Attribution Campaign for Google Search. The issue is when I add the click through URL in the Ad Group. I get an error message that says 'Enter a valid Amazon URL beginning with.......' (See screenshot). This is exactly what I have done, I've added the link for my product detail page on Amazon which is an Amazon URL. I've got no idea how to solve this problem - anyone got any suggestions?? Thanks