Google Maps is the new way to respond to messages

Google News Flash
Google Maps MessengesBeginning July 2022, the Google My Business mobile app will no longer be available, and the Google Maps app will be the best place for replying to customer messages on mobile.
Turn on your notifications to ensure you’re notified by email and Google Maps push notifications for new incoming messages. You can also respond to messages from your Business Profile on Google Search.

Steps to see your messages in the Google Maps app:
1. Open the Google Maps app on your mobile
2. Tap Updates > Messages > Business

Visit the Google Help Center for Detailed Information