No idea if this is helpful, played with all this and another POD provider app tonight. Found the answer for me at least. Here’s what helped on my WordPress install…. It is working now. Copied from another place below.
UPDATE:
I played with WordPress & some things all night.
Seems I have things working correctly now.
Problem was a number of WordPress caching plugins.
Specifically W3 Total Cache, and some other stuff, not sure exactly, but can now copy Printful listings from other platforms to WordPress/Woo successfully, and create new products and get mockups to push to Woo.
Anyway, long story short – caching plugins caused problems. Or maybe it was an image optimizer plugin like EWWW Image Optimizer….
No idea…. At least it’s working.