Problem with Permalink and feed url

I installed the plugin, which generates a simple permalink:
https://example.com/?feed=amazon-pollycast

However, by inserting the feed link on blueprints, the following message appears:
Please enter a valid url ending with “/ amazon-pollycast”.

Unfortunately, I cannot change the structure of the permalink (to “https://example.com/feed/amazon-pollycast”).

Is there any way to use on blueprints “*/?Feed=amazon-pollycast”?
Thank you.