You will need to specify several details for the relay client so it can connect to this custom webhook server. Create a new file called transponder.sh and specify these variables:

export RELAY_API_ADDRESS=http://your-server-domain:9301
export RELAY_KEY=cbcf9ee2-7fd2-4e2c-aa59-9c3fc441fdd4
export RELAY_SECRET=change-me
export RELAY_GRPC_API_ADDRESS=your-server-domain:9302    

Now, source them:

source transponder.sh

To start using your new self-hosted Webhook Relay server:

relay forward -b my-bucket http://localhost:8080

If you run the agent as a background process, check out the configuration file.