QStash requires a publicly available API to send messages to. The recommended approach is to run a development server locally and use it for development purposes. Alternatively, you can set up a local tunnel to expose your API, enabling QStash to send requests directly to your application during development.

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localtunnel.me

localtunnel.me is a free service to provide a public endpoint for your local development. It’s as simple as running 
npx localtunnel --port 3000
replacing 3000 with the port your application is running on. This will give you a public URL like https://good-months-leave.loca.lt which can be used as your QStash URL. If you run into issues, you may need to set the Upstash-Forward-bypass-tunnel-reminder header to any value to bypass the reminder message.

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ngrok

ngrok is a free service, that provides you with a public endpoint and forwards all traffic to your localhost.

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Sign up

Create a new account on dashboard.ngrok.com/signup and follow the instructions to download the ngrok CLI and connect your account: 
ngrok config add-authtoken XXX

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Start the tunnel

Choose the port where your application is running. Here I’m forwarding to port 3000, because Next.js is using it. 
$ ngrok http 3000



Session Status                online
Account                       Andreas Thomas (Plan: Free)
Version                       3.1.0
Region                        Europe (eu)
Latency                       -
Web Interface                 http://127.0.0.1:4040
Forwarding                    https://e02f-2a02-810d-af40-5284-b139-58cc-89df-b740.eu.ngrok.io -> http://localhost:3000

Connections                   ttl     opn     rt1     rt5     p50     p90
                              0       0       0.00    0.00    0.00    0.00

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Publish a message

Now copy the Forwarding url and use it as destination in QStash. Make sure to add the path of your API at the end. (/api/webhooks in this case) 
curl -XPOST \
    -H 'Authorization: Bearer XXX' \
    -H "Content-type: application/json" \
    -d '{ "hello": "world" }' \
    'https://qstash.upstash.io/v2/publish/https://e02f-2a02-810d-af40-5284-b139-58cc-89df-b740.eu.ngrok.io/api/webhooks'

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Debug

In case messages are not delivered or something else doesn’t work as expected, you can go to http://127.0.0.1:4040 to see what ngrok is doing.