Open "SMS/Phone" doesn't appear in app window

Dear Sir or Madam,
When I click on the Join Chrome extension on my other computer, a window pops up. That window says 3 things across the top. Devices, Notifications & SMS/Phone.
On my second computer, when I click on the Join extension, the first 2 are visible at the top of the app pop up - but "SMS/Phone" does not appear.
Please advise me what I must do to gain this functionality on my second computer.
Thank you in advance!