Motor driver will disarm in RCin but not Throttle mode

I have been working on my 1st rover and I have run into a issue.

I have got my rover driving with RCIN3 but when I change it to throttle rather then RCIN3 the Motor Driver will not disarm anymore.

I can also set both inputs to groundsteering mode and I can get it to disarm.
However that doesn’t help me as I still don’t have a throttle.
So I think there is something different about throttle servo setting.

Is there a setting I need to change to get the throttle to work?
Or should I be using a different mode?

I have attached a screenshot of my settings and a link to the Motor Driver I am using as well.
I have moved around the trim to set the mid point to 1500 and set the upper and lower to 900-1100 and 1900-2100 respectively.

Servo page:

Motor Driver:
https://www.aliexpress.com/item/1005001804944223.html?spm=a2g0o.order_list.order_list_main.5.56021802123B6S