Mission Planner plugin didn’t see type Locationwp from MissionPlanner.Utilities namespace

I’m trying to add plugin with button which allows to change altitude to a specific one. Code is pretty straight forward -

Host.comPort.setNewWPAlt(new Locationwp {alt = newalt / CurrentState.multiplieralt});

However, when I start MP I see error in logs that there no Locationwp type in MissionPlanner.Utilities namespace.

Any help/tips appreciated

Full code and error messages would be helpful