How to get passcode for airplay?

If an AirPlay passcode has been set for the Apple TV, and is requested on your iPhone, it should appear on the TV screen for you to use.

If an AirPlay password (different from a passcode) is being requested, then it had to be set by someone with access to the Apple TV. The Password would only be known to whoever set it. However it can be changed without knowing it from the Apple TV Conference room settings:

Use Conference Room Display mode and related settings on your Apple TV - Apple Support

Settings > AirPlay > AirPlay, and select Require Code under Security

As said, go into the Apple Tv settings as explained above, and make sure it is set for a "passcode" and not a "password".

If its set for a "password" it will not appear on screen.

Settings->AirPlay->Security and make sure its set to "Passcode", rather than "password".

Click here for details:

https://support.apple.com/en-us/HT202618

So is there a passcode or a password set then? Is your iPhone asking for a passcode or password, and none appears on the TV, then its likely a Password, and only whoever set it would know it.

If this is your Apple TV, make sure passcode is correctly set in the Apple Tv settings.