The central spout is blocked.
Clean the coffee pipework.
You can also start the Rinse appliance function manually (depending on the model).
Is there still no coffee flowing out of the central spout or is it only dispensed via one side?
Dismantle the central spout and clean all parts carefully. Use the supplied cleaning brush for parts that are difficult to reach.
Clean the steam nozzle with the cleaning brush.
Make sure that all the individual parts of the central spout are assembled correctly.