If you are getting the 'Oh no' pop up then follow these steps to get things back on track.
Things to know:
Follow these steps in order one by one.
Try to send a text after each step to see if the issue is resolved.
If the issue is not resolved, then move onto the next step.
Step 1: Close/re-open your browser
Step 2: Log in/out via the Account Settings Page
Step 3: Reinstall the Chrome extension by clicking 'Remove' and then 'Add' (make sure to close/reopen your browser afterwards).