HomePod mini & Iphone issue

Have you updated the iPhone and the HomePod to the latest software?

Note: To hand off audio, your device must have Bluetooth turned on and be on the same Wi-Fi network as HomePod.

• On your iPhone in Settings- General - AirPlay & Handoff, makes sure Transfer to HomePod is enabled. If it is enabled, toggle it off, restart your iPhone, then turn it back on. In any case it’s a good idea to restart your iPhone if it’s not working anyways, If it still won’t work try restarting the HomePod via the Home App- HomePod Settings.

Play audio on HomePod using an iOS or iPadOS device - Apple Support