Answer
If your end users are receiving the "Invalid Reply URL" error when trying to sign in to Foxit check the SP Assertion Consumer Service URL value in Azure. This value is copied from the Directory settings in the Admin Console.
Navigate to the Admin Console - Settings - Directory Settings - Click on "More" in the Actions column - Directory Settings - Next - Check the value of the SP Assertion Consumer Service URL to see if it matches what is in Azure. If it does not match, please copy this value and paste it into the field in OK.
Have your users try to sign in the issue should be resolved.