The issue with the prototype among users from the USA

We encountered a problem while testing the prototype. The prototype opens and works for users in Europe, but users in the USA see a green screen. Can you suggest what this might be related to?

Hi there! Thanks for flagging this, this looks odd. Users in USA should also see the prototype if you have given access to the file.

Can you share us if there is any error message on their end? Is it happening in the browser, desktop app or both?
For quick fixes, can you please ask them to force-quit and open Figma in a new browser window (or force-quit the Figma Desktop app and restart it.) and clear out the cache? Here are some information to troubleshoot: https://help.figma.com/hc/en-us/articles/360040523973-Troubleshooting-checklist

If this doesn’t help, I’d suggest you to reach out directly to the support team by filling this form here: https://help.figma.com/hc/en-us/requests/new , so we can try to replicate it. Be sure to use your Figma account email, include links to the file, and share it with support-share@figma.com. Thank you