Implementing a "keepAlive" call to Betfair's API

I am trying to implement a “keepAlive” call to Betfair’s API and thereby keep my session alive. Unfortunately, I am having some difficulty, and I am hoping that someone here can help me.

(Please see the attached images for information from Betfair’s documentation on keepAlive)

I have attempted the following, but while I get a response, it is not the response I am supposed to get according to the documentation:

urlAlive = "https://identitysso.betfair.com/api/keepAlive"
headers = Dict("X-Application" => strip(appKey), "X-Authentication" => strip(sessionToken), "content-type" => "application/json")
body = HTTP.escapeuri(headers)
res = HTTP.request("POST", urlAlive, body=body)

I get the following response:

“”"
HTTP/1.1 200 OK
P3P: CP=‘IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT’
Pragma: no-cache
Cache-Control: no-cache,must-revalidate,no-store
Expires: Thu, 01 Jan 1970 00:00:00 GMT
Content-Type: image/png
Content-Length: 69
Date: Wed, 05 Aug 2020 19:41:10 GMT
Content-Security-Policy-Report-Only: default-src ‘unsafe-inline’ ‘unsafe-eval’ data: https: wss:; report-uri https://shk.betfair.com/csp
X-XSS-Protection: 1; mode=block![keepAlive_1|690x351]

69-byte body
“”"