hi mdi,
Poly edge b20 is a certified zoom phone device and will auto provision if the following conditions are present. First, phone is either a new phone out of the box and has not been used on some other system or you reset the phone to factory. Second, your firewall rules permit the phone to reach both poly and zoom.
https://support.zoom.us/hc/en-us/articles/360001299063-Zoom-Phone-Certified-Hardware
Check to see that your firewall has the appropriate rules for poly and zoom as specified by poly and zoom in the links below. zoom will let poly know that your poly phone is registered with zoom. your poly phone will contact poly first, poly tells the phone where to go to get its provisioning (in this case to zoom) and then zoom takes care of the provisioning. You should take a look at the firewall logs to see activity between the poly phone and your firewall.
https://support.zoom.us/hc/en-us/articles/201362683-Zoom-network-firewall-or-proxy-server-settings
https://docs.poly.com/bundle/pdms-sp-ag-current/page/required-ports-and-trusted-ip-addresses-and-hosts.html
for more information, please visit these zoom links.
https://support.zoom.us/hc/en-us/articles/360033223411-Getting-started-with-provisioning-desk-phones
https://support.zoom.us/hc/en-us/articles/360021119092
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thanks, eliot