Noob here, need help on setting up differential thrusting(skid steering) on an airboat

Hi everyone, I am very new to this hobby and I’m currently trying to build a dual motor airboat with differential steering. I’ve looked at many posts but they didn’t help that much. I set my frame class as 2 and frame type as 0. I also set up my servo 1 as throttle_left and servo 2 as throttle_right, but they don’t seem to drive the motor at all. Here is what my interface looks like.

According to other posts on the forum this seems to be the correct setup but mine doesn’t work. However when I set servo 1 and servo 2 as motor1 and motor2 they actually spin when armed.

How exactly should I set up differential thrusting and skid steering? I am very new to this hobby so it would be great if anyone can have a screenshot of the servo output setup. Much thanks