Posting to Activity

I'm trying to make posts to Activity with the following request:

jQuery.ajax("https://imistour3747.imiscloud.com/api/Activity", {
type : "POST", data : {
"$type": "Asi.Soa.Core.DataContracts.GenericEntityData, Asi.Contracts",
"Properties": {
"$type": "Asi.Soa.Core.DataContracts.GenericPropertyDataCollection, Asi.Contracts",
"$values": [
{
"$type": "Asi.Soa.Core.DataContracts.GenericPropertyData, Asi.Contracts",
"Name": "ACTIVITY_TYPE",
"Value": "MEETING"
},
{
"$type": "Asi.Soa.Core.DataContracts.GenericPropertyData, Asi.Contracts",
"Name": "PartyId",
"Value": "23226"
}
]
}
},
contentType: "application/json",
headers: {"RequestVerificationToken": document.getElementById("__RequestVerificationToken").value},
success: function(data){console.log(data);}
})

I'm going off the information in this discussion board https://developer.imis.com/discuss/5c4f173459c7d00020810d4b

But I always receive a 500 error, has anything changed with posting to activity in 20.3?