In addition to verifying that the user's sign-in credentials are correct, you should make sure that you enter the Session Initiation Protocol Uniform Resource Identifier (SIP URI) in the following format in both the Account and User Name fields. The Account and User Name fields must be identical.
User Name: email@example.com
Note The placeholder <firstname.lastname@example.org> represents the user's sign-in credentials.
Step 3: Check the device's firmware version
Check that the device's firmware version is at the minimum level for connection to Skype for Business Online. To view a list of supported minimum firmware revisions, go to the following Microsoft website:
Note If the user doesn’t have an Office 365 license that enables public switched telephone network (PSTN) dial-in or dial-out and intends to use the device for Voice over IP (VoIP) calls to other Lync or Skype for Business Online endpoints, the minimum firmware level across the devices should be 4.0.7577.4451.
To see what firmware version is installed on the Aastra 6725ip, HP 4120, Polycom CX600, or Polycom CX3000, select Menu on the Home screen, and then select System Information. For the Polycom CX700, tap Advanced on the Home screen, and then tap System Information. You may have to scroll down to see the Version field.
If your device doesn't have the minimum version installed, you must upgrade your device. If you have access to a Lync on-premises environment that's configured for device updates, you can update the device by signing in to the on-premises environment. If you don't have a Lync on-premises environment, you must contact the manufacturer of your phone.
Step 4: Verify that there is no authentication proxy
Lync Phone Edition devices don't support authentication proxies between the device and the Skype for Business Online endpoint. Contact your IT department to see whether the network requires an authentication proxy.
To work together with Office 365, your Lync Phone Edition device must be tethered to a Windows client computer to which a Lync delegate is signed in.
This issue can occur if the sign-in information is incorrect, if the device isn't running a firmware version that's supported by Skype for Business Online, or if there's an authentication proxy between the device and the Skype for Business Online endpoint.
Collect Lync Phone Edition logs
Before you contact Skype for Business Online Technical Support, collect log files from the Lyne Phone Edition device. For more information, go to the following Microsoft website:
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.