I am getting the same result with my refurbished Pebble 2 + HR on my iPhone 6 running iOS 11.0.3 on Verizon.
It was just yesterday, after a week of struggling and trying many actions, that I finally got the carrier verification and Text Replies (canned only) set up and gained access to the server.
It appears that the only function still not working as expected is the microphone for Voice Dictation and Voice Text Replies.
I didn’t receive an instruction manual with my refurbished Pebble 2 HR.
Any guidance to resolve this would be greatly appreciated.