Logstash filter: copying values after split

[fringeadmin (N)]

I have azure event hub data coming into logstash via the eponymous plugin. I get huge junks of json that contain multiple events which I then have to split into distinct events. Here is a simplified example:

{"records": [
{ "LogicalServerName": "myservername", "SubscriptionId": "mysubid-uuid", "ResourceGroup": "Prod", "time": "2019-02-15T17:44:23.3870000Z", "resourceId": "/SUBSCRIPTIONS/mysubid-uuid/RESOURCEGROUPS/PROD/PROVIDERS/MICROSOFT.SQL/SERVERS/myservername/DATABASES/MASTER", "category": "SQLSecurityAuditEvents", "operationName": "AuditEvent"},
{ "LogicalServerName": "myservername", "SubscriptionId": "mysubid-uuid", "ResourceGroup": "Prod", "time": "2019-02-15T17:44:23.3870000Z", "resourceId": "/SUBSCRIPTIONS/mysubid-uuid/RESOURCEGROUPS/PROD/PROVIDERS/MICROSOFT.SQL/SERVERS/myservername/DATABASES/MASTER", "category": "SQLSecurityAuditEvents", "operationName": "AuditEvent"}
]}

After the split I'm trying to copy the key LogicalServerName into a custom field called sourceHost. This is to normalize the input from a variety of services. Unfortunately, it doesn't seem to work. Records.LogicalServerName has the correct value, but the sourceHost field is just blank.

Here's the filter I'm trying to use:

filter {
    if [type] == "azure_event_hub" {
        json {
            source => "message"
        }
        split {
            field => ["records"]
        }
        mutate {
            # Map the requestHost to a standard hostname field
            copy => { "records.LogicalServerName" => "sourceHost" }
        }
    }
}

What am I missing here?

[Badger]

Try

 copy => { "[records][LogicalServerName]" => "sourceHost" }

[fringeadmin (N)]

That was the magic! Thank you very much. I must not have been googling the right things, because that never came up as one of the dozen or so things I tried.