This means we're getting this response from Goolge servers, which means there's a problem with your API Key.
Solution: Create a new API KEY.
Step 1: Open the Google Services page.
Step 2. Enter your App name or choose it from the list, then enter any package name for example any.test and finally click on Continue:
Step 3: Click on Enable Google cloud messaging
Step 4: Finally copy the API key and Sender ID.
Step 5: Go to your PushBots dashboard in app settings, and update your Chrome API KEY