Dishwasher not draining

It can be several things. The first thing to do is remove the bottom filter inside the unit and check it for blockage. Wash it out well. After that, check the drain line has no objects in it and make sure it is in a hi loop by the sink. This means the hose is higher than the drain, so dirty stale water doesn’t backflow into the unit. Many times the drain falls too low, and people don’t realize it. The last thing is a faulty drain pump, that if broken, will need service to replace.