excel - VBA GET request failing, bad format? -

i'm novice , has been amazing far! have issue request sso authentication in excel visual basic script. api says send request to:

https://services.example.com/api/security.svc/ssositelogin/siteid/enterpriseguid/authtoken/timezoneoffset

where values siteid, enterpriseguid, authtoken, , timezoneoffset have been obtained previous requests, have worked fine. when send final request security token, returns:

{"detail":"ssositelogin failed.input string not in correct format."}

here relevant code:

dim hreq new winhttprequest dim response string dim url string     'get security token url = "https://services.example.com/api/security.svc/ssositelogin/siteid/enterpriseguid/" & authtoken & "/null" hreq.open "get", url, false hreq.send  response = hreq.responsetext range("a13") = response 

the siteid , enterpriseguid variables input code, , authtoken stored earlier post request. last value, timezoneoffset, given "null" earlier request i've been typing "/null" @ end i'm concerned that's what's triggering incorrect format response. else returns total error server though.

any ideas? thank in advance!

i had put values cells , sending request "range("e5") & "/" & range("e6") & "/", etc. try couple of debugging issues without having go vba editor , reason worked! ended using string "null", too. if knows why worked , inputting 1 string doesn't i'd interested find out.