Thanks for your help guys, I was stuck on this for ages.
I’ve since found a solution on stack overflow -> curl -G -v http://x.x.x.x/cr --data-urlencode pw=password --data-urlencode t=[0,0,0,0,0,0,1200,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0]
Apparently, I needed to encode the data.
Now I have an awesome Switch to fill up my pool (OpenSprinkler).
The switch changes color while filling so I know it’s working