I have looked at https://ovc4x.ovcirrus.com/api/openapi but it doesn't have anything regarding UPAM or accounts.
I found some old API request inside github script for Employee accounts but when I try to call it using this:
/api/ham/userAccount/getAllAccountList
I get this error which state it's deprecated
{"result":"success","errorCode":-1,"errorMessage":"upam.deprecatedAPI","data":null,"translated":{"resultTranslated":"success","errorCodeTranslated":"-1","errorMessageTranslated":"Deprecated API, the interface will no longer be maintained","messageObjects":{}}}
In order to get the guest account listed in OmniVista 2500, please uses these following requests. Be sure to be authenticated before using this request.