[BUG] App is running, but error response in Event Subscriptions setup

[pixeldevsio]

Describe the bug

• I have the app running on a non-local server. I see it running in my console.
• I uploaded all the files from Github to the server to https://mydomain.com/slack/events.
• I then ran the appropriate commands to install the app.
• I finally ran npm run serve and it served the app with this response.

[DEBUG]  bolt-app Initializing HTTPReceiver
[DEBUG]  web-api:WebClient:0 apiCall('auth.test') start
[DEBUG]  web-api:WebClient:0 will perform http request
⚡️ Bolt:	App is running!
[DEBUG]  web-api:WebClient:0 http response received

• I go to the Event Subscriptions on api.slack.com for my app and add the URL above.
• I get this as the response

Request URL Your URL didn't respond with the value of the challenge parameter.

• I opened it up in Postman and sent an HTTP POST request to the url and receive a 403 error (kinda expected since theres no index file in the build)

What am I doing wrong?

Requirements (place an x in each of the [ ])**

• [x ] I've read and understood the Contributing guidelines and have done my best effort to follow them.
• [x ] I've read and agree to the Code of Conduct.
• [x ] I've searched for any related issues and avoided creating a duplicate issue.

To Reproduce

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Expected behavior

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Reproducible in:

package version: 8.3.0
node version: 17.3.0
OS version(s): Ubuntu Linux

Additional context

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