First, I suggest that you split your command into separate commands. There is no need to put all changes in one command. You can do:
/cs?pw=xxx&sid=xx&st=xx&sd=xx
first to set the special station attribute of that zone
and in a separate command you can do:
/cs?pw=xxx&q0=xx&m0=xx
to set sequential bitfields, and master operation bitfield. Please note that the /cs command has no parameters named ‘stn_seq’. The parameter you should be using is q0, and it’s a bit-field (i.e. it sets sequential bits for a set of 8 zones at a time). Check the API document to see the available parameters:
https://openthings.freshdesk.com/helpdesk/attachments/5114870617
You said you “cannot figure out how to enable the master1/master2 flags”, can you be more specific about what’s the symptom? What’s the result you get when you run the command. If it’s successful, what did it end up changing and how does it differ from what you intended?