Why is stop level required in update_open_position API endpoint?

[wki]

Hi, I am struggling to figure out why IG Rest API is asking for a stop_level when I am trying to update the trailing stop.  This is the python code I am trying to run:
response = ig_service.update_open_position(deal_id='XXXXX',limit_level=None, stop_level=None, trailing_stop=True, trailing_stop_distance=25, trailing_stop_increment=1)
print(response)

output:

IGException: {"errorCode":"validation.not-null-conditional-set-value.request"}

If I change stop_level to: latest price - (the trailing_stop_distance + trailing_stop_increment) then it updates ok, but why do I need to specify the stop_level if its a trailing stop?  The stop_level will change as the price goes up and it shouldn't make a difference what I provide as stop_level surely, as long is the trailing_stop_distance meets the rules?  Am I missing something?  When I created the trade via the create_open_position endpoint, I had stop_level = None and a stop_distance and it went through ok.

Edited June 5, 2023 by wki