There are several reasons you may not be receiving interactions even if you are logged in, and set to online in the queue. Some of the most common answers can be found in the table below.

Agent is not in the correct groups
The most likely scenario is the user is not in the correct user group. Interactions are routed to Queues, which has user groups assigned to them. If the user is not a member of a group, they will not be assigned any interactions. You can assign users to a group by visiting the /groups page in your application available under the User Groups page found in the Settings submenu
Agent has incorrect media channels
If the company is using task router - they may have the incorrect task router channels and be unable to access a particular interaction type. This can be checked by editing a user:
Mitel is misconfigured
If this is am Ignite Agent, the engage queue may not correctly linked to the Ignite queue correctly. Verify the queue is correctly linked in the edit queue page.