You might see "Please install GrassBlade LRS and configure the API credentials to use this LRS Management Page" if:
1. cURL is not installed or configured for PHP.
2. You are on a host like WPEngine which sometimes blocks requests.
3. Your server is configured with a local IP, and the server is not able to make a call to itself. If its a VPS or dedicated server, you could add your domain in hosts file with 127.0.0.1 loopback IP.
NOTE: If you are see this issue, you might be having issue with Triggers and Completion Tracking. Please make sure you test and see if that is working fine.