KQL json mapping from Date Pipeline

Hi everyone.

I’m running into an issue when ingesting data from MongoDB into my Kusto database using Azure Data Factory’s Copy Activity. Two of the fields in my source collection are Unix timestamps, but when they arrive in Kusto they end up stored as long instead of datetime.

To fix this, I created a JSON ingestion mapping on my Kusto table that should convert those two timestamp columns into proper datetimes during ingestion. However, when I specify that mapping in the Copy Activity’s Sink settings, I get the following error:

ErrorCode=KustoMappingReferenceHasWrongKind
Type=Microsoft.DataTransfer.Common.Shared.HybridDeliveryException
Message=Mapping reference should be of kind 'Csv'. Mapping reference: 'UnixToDateTimeMapping'. Kind 'Json'.
Source=Microsoft.DataTransfer.Runtime.KustoConnector

 I’ve tried passing the mapping name and adding various sink properties, but I can’t get ADF to apply my JSON mapping. Has anyone successfully configured a Copy Activity to use a Kusto JSON ingestion mapping? 

The code of my mapping as well

.create-or-alter table info_connections_teste ingestion json mapping "UnixToDateTimeMapping"
'['
'    { "column":"_id",               "datatype":"string",   "Properties":{"Path":"$._id"} },'
'    { "column":"latency",           "datatype":"real",     "Properties":{"Path":"$.latency"} },'
'    { "column":"packetloss_percentage","datatype":"int",   "Properties":{"Path":"$.packetloss_percentage"} },'
'    { "column":"download_occupancy","datatype":"real",     "Properties":{"Path":"$.download_occupancy"} },'
'    { "column":"upload_occupancy",  "datatype":"real",     "Properties":{"Path":"$.upload_occupancy"} },'
'    { "column":"connection_id",     "datatype":"string",   "Properties":{"Path":"$.connection_id"} },'
'    { "column":"createdAt",         "datatype":"long",     "Properties":{"Path":"$.createdAt"} },'
'    { "column":"createdAtDate",     "datatype":"datetime", "Properties":{"Path":"$.createdAt","Transform":"DateTimeFromUnixSeconds"} },'
'    { "column":"updatedAt",         "datatype":"long",     "Properties":{"Path":"$.updatedAt"} },'
'    { "column":"updatedAtDate",     "datatype":"datetime", "Properties":{"Path":"$.updatedAt","Transform":"DateTimeFromUnixSeconds"} },'
'    { "column":"__v",               "datatype":"int",      "Properties":{"Path":"$.__v"} }'
']'