hamilton beach flexbrew 2-way coffee maker won't brew into my travel mug on the single-serve side, just drips into the tray

Make sure you're using the single-serve side correctly. First, check that the travel mug is placed correctly under the outlet.

Second, ensure you've selected the correct brew option for a mug on the control panel.

If you're brewing a small batch of 1-4 cups into mugs, you need to use the small batch mode for optimal flavor and proper function.