It relates to a dial plan.
From Lync control panel:
Open your Dial Plan and you should see a field called "Dial-in conferencing region" it's probably blank.
Put something in there and commit it. It should flow through to the Dial In Access Number section.
It does sound like you have some services missing.
Open Topology builder and download your current topology.
Browse to the pool and check that conferencing is enabled.
If not, enable it and publish your topology.
You will need to run the Lync Deployment Wizard again to finish the deployment

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