Some Flow extensions use Salesforce public API’s. They basically go out from your org, into the Internet, and then back into Salesforce. When they do this, they run into some of the web security that Salesforce uses to protect your org. These registrations are called Remote Site Setting. For API’s on the public surface of your org, you have to register the URL of your own org onto your org. (If this sounds strange, you’re not alone.)
If you haven’t done this and you try to run a Flow with an extension that uses these apis, you’ll see an error. Here are a couple of examples of how this error might show up:
To address this, copy the initial part of the endpoint in the error message to the clipboard. in the example above on the right, that would be
To address this, copy the root url from the error message and go to Setup –> Remote Site Settings. Create a new setting and paste the URL there:
This configures your org to essentially allow applications to run that call out to the internet and then back into the same org via its api endpoints.