OK, looking further, I’m seeing a couple JavaScript errors in the console for your site. Screenshot:
https://d.pr/i/3T4zkR/wedkPHCMH7
They seem to be coming from the QR Code Tag plugin you have installed. Can you please deactivate that plugin temporarily and see if the Amazon button returns?
If not, try a full conflict test:
- Temporarily switch your theme to Storefront
- Disable all plugins except for WooCommerce and Amazon Pay
- Repeat the action that is causing the problem
If you’re not seeing the same problem after completing the conflict test, then you know the problem was with the plugins and/or theme you deactivated.
To figure out which plugin is causing the problem, reactivate your other plugins one by one, testing after each, until you find the one causing conflict. You can find a more detailed explanation on how to do a conflict test here.
Let us know, thanks! ??