Adding contact to contact list using API 2.5 query

Hey! I am working on the query using Qualtrics API 2.5, which would add contact to contact list. I struggling with adding custom embedded data to the query. I have added manually this embedded data to list, and now i would like to know what is the query syntax to put the value into it. It is pretty simple for existing embedded data like FIrstName and LastName. My query looks like this ( pls don't focus on the focus on the beginning, it's just a concept.) In the below concept i would like to put specific value (SV_XXXXXX) to embedded data named SV. How it should be written? www.XXXXXXXXX&FirstName=Piotr&LastName=Siudak&SV=SV_XXXXXX