Hi Brigid94,
Make sure you are still using the steps to AirPlay to your HomePod as mentioned here:
1. To open Control Centre on your iOS or iPadOS device, do one of the following:
* On iPhone with Face ID or on iPad: Swipe down from the top-right edge.
* On iPhone with a Home button: Swipe up from the bottom.
2. Tap the audio card, tap
, then select one or more HomePod speakers.

To play audio from other devices that support AirPlay 2, see the documentation for that device for details about selecting an audio destination.
You can find these steps along with other information that may be helpful, here: Play audio on HomePod using an iOS or iPadOS device – Apple Support
If you have followed the steps correctly and you still have the issue, let us know if you get any specific alerts or error messages when trying, as those may help us determine what might be causing the issue.
We also recommend restarting your devices and keeping them updated as those steps assure you have cleared out any minor software issues and are running the most current version.
Restart your iPhone - Apple Support
Update your iPhone or iPad - Apple Support
If HomePod or HomePod mini isn't responding - Apple Support
If you still have questions, reach out to Apple Support directly, as this may require closer guidance: Get Support
Cheers!