Urgent help - no connection error *solved*

See the community FAQ:

Why Did My Integration/SmartApp Stop Working in January 2023?

ST isn’t trying to force you to stop using Notify Me When. Rather, they have transitioned to a new architecture which no longer supports it. So it just won’t work.

The good news, as @orangebucket mentioned, is that in the new architecture basic routines have better notification capabilities than they used to, and may be all you need. But again, read the FAQ and it should answer most questions.