...

This option can provide a more streamlined payment flow for paid apps on itch.io. Warning: tHis This will not work for apps that are free download only on ithcitch, please verify your workflow can work before continuing.

Essentially this option will send your users to <YOUR_ITCH_URL>/purchase?popup=1 instead of just <YOUR_ITCH_URL> e.g. https://myron.itch.io/deisim/purchase?popup=1 instead of just https://myron.itch.io/deisim

...

11. Screenshots

Add several screenshots to your app listing. You can click a screenshot to remove it.

...