I'm embarrassed to admit that I spent about an hour on this problem today so I thought I'd share the solution just in case someone else finds themselves in a similar situation.
THE PAYPAL CUSTOM PAYMENT PAGES FUNCTION NO LONGER WORKS! STOP TRYING TO FIGURE OUT WHAT IS WRONG! The big question is why does Paypal still have this function described in their developers guide with full instructions????
As a work-around you can use
image_url parameter to set your image logo (size 150×50) in the checkout page. It's actually easier than the deprecated
image_url=https://xxxxx.com. Of course, the xxxxx is going to be replaced with your real image url. And, of course, always use https.
There, hope that helps someone.