App Submission Repeatedly Rejected because tester is getting 'Site can't be reached" error

[samsappsdev]

Hey everyone,

Having problems with my app submission getting rejected two times now for OAuth errors, but can't figure where the errors are coming from. The app installation process is working on my end for my test stores. In the screenshot, it appears that the tester isn't even reaching the app server https://hammerhead-app-4slw6.ondigitalocean.app/, as they're getting a "The site can't be reached" error. However, I've tried reaching the server from multiple IP Addresses now on my end and have been able to reach it. The error screenshot is https://shopify.click/95444-35905-53641-86879-21425.png. Was wondering if anyone else has encountered an issue like this and/or knows where to go with this.