Hi and welcome to the forums.
Please read point 11 here about formatting your post correctly.
You need to split the resource into these parts:
switch:
platform: rest
name: luxaflex open
resource: http://192.168.178.241/blinds/?
body_on: 'ws=50'
body_off: 'ws=90'
If there is some way you can interrogate the blind for its current state it would also be beneficial to add an is_on_template https://www.home-assistant.io/integrations/switch.rest/#is_on_template