Struggling with the cyclic reference error

Your first steps are correct

let
    userCount = Json.Document(Web.Contents("https://storfolloikt.pureservice.com/agent/api/user/count", 
        [
            Headers=[
                Accept="application/vnd.api+json",
                #"X-Authorization-Key"= Text.From(#"PUSapikey")
            ]
        ]))[count],
    pages = Number.RoundUp(userCount / 500),

but then you veer off track. Next step is to create a list with all the URLs you need to fetch the data chunks.

since you already know the number of pages you need there is not really a reason to use list.generate any more. A simple 

{1..pages}  

is enough.  Convert that to a table, add your GetUserData function as a custom column, and combine the output.