We need to define the model inputs first.
1. In the Input panel double click on Raster layer.
2. In the Raster Layer Parameter Definition dialogue type Filled DEM as Description and keep the Mandatory box checked.
3. Click OK.
4. Double click on Number in the Input panel.
5. In the Number Parameter Definition dialogue type X Coordinate Outlet as Description, keep Float as Number type and leave everything else as default.
6. Click OK.
7. Do the same for the Y Coordinate.