Navigate to Settings → Download Clients.

In Download Clients:

• Click on the Plus button.

Click on one of the buttons to add that type of Download Client:

• If adding a Download Client that supports the Usenet click on the Usenet buttons.
• If adding a Download Client , click one of the Torrents buttons

• Name: NZBGet.
• Enable: Checked.
• Host: 172.19.0.37. This is the ipv4_address as defined for NZBGet in the Dockerfile.
• Port: 6789: This is the Port as defined for NZBGet in the Dockerfile.
• Url Base: <blank>.
• Username: nzbget.
• Password: tegbzn6789.
• Category: Series.
• Recent Priority: Normal.
• Older Priority: Normal.
• Add Paused: Not Checked.
• Use SSL: Not Checked.
• Client Priority: 2.
• Click Save.

Click on the Test button at the bottom:

During the test, the button will change as:

If successful, the button will show: