Thanks for reaching out. Let's sort this out.
Quick questions: what type of Chromecast device do you have? Are you using a G Suite or Google Workspace account in setting up your Chromecast? if yes, please use a regular Google Account and check if you will be getting the same issue. Reinstalling the Google Home app and rebooting your mobile phone might also help.
We want to ensure you are good to go, and everything is working properly. Please let me know if you are still having trouble, as I will be locking the thread in 24 hours due to inactivity.