Use a different app, like Amethyst or Onyx. If they can use the NWC connecting string fine, then its a problem with Damus.

If they also fail to parse it or use it, its a problem with the connection string. Check if there are weird characters in the connection string, like slash after the relay URL, or extra spaces / commas.

Dealt with a few of those myself when adding NWC to Oak Node recently.