Enter the following for the Remote Site URL: https://XXX--tgtx-retention.vf.force.com, updating the XXX with your custom domain.
Example: https://myschool--tgtx-retention.vf.force.com
You can find your custom domain name by navigating to your Student Success Center and copying it from the URL:

Enter the following for the Remote Site URL: https://XXX.naYY.visual.force.com, updating the XXX with your custom domain name and YY with the value for your Salesforce instance.
Example: https://tgtx-retention.na30.visual.force.com
Note: If using a SANDBOX, replace "na" with "cs."
You can find your custom domain name by navigating to your Student Success Center and copying it from the URL:

Notes about Remote Site Settings: