How to properly pass the session_id to GA4 via Measurement protocol - google-analytics-4

Question

GA4 purchase events are sent from client server via measurement protocol. But there is no session_id parameter in the queries, because of that source and medium is lost. We tried to pass the session_id parameter in MP request, but no data were received.
Example of submitted request:
{
"timestamp_micros": "1664522406546590",
"non_personalized_ads": false,
"events": [
{
"name": "purchase_balance_top_up",
"params": {
"user_id": "11111111",
"crm_id": "11111111",
"balance": 990,
"payment_method": "paymore"
}
}
],
"client_id": "1119492379.1652295143",
"session_id": "1664522264",
"user_id": "11111111"
}
Attaching a screenshot of the raw data from BigQuery on events sent by MP.
Screenshot of the raw data from BigQuery
Help, how to properly pass the session_id? Or how to make sure that events don't lose source param?

Answer 1

We found a solution to the problem. It's simple. The parameter "session_id" must be passed inside the array "params" of the event.
Here is an example of the correct event data array to be sent via measurement protocol:
{
"timestamp_micros": "1664522406546590",
"non_personalized_ads": false,
"events": [
{
"name": "purchase_balance_top_up",
"params": {
"user_id": "11111111",
"crm_id": "11111111",
"balance": 990,
"payment_method": "paymore",
"session_id": "1664522264"
}
}
],
"client_id": "1119492379.1652295143",
"user_id": "11111111"
}

Answer 2

Actually we are sending purchase events similarly with such request:
{
"client_id": "xxx.xxx",
"user_id" : "xxxx",
"non_personalized_ads": false,
"user_properties": {
"user_id_dimension": {
"value": "xxxx"
}
},
"events": [{
"name": "purchase",
"params": {
"currency": "USD",
"transaction_id": "T_12345",
"value": 12.21,
"engagement_time_msec": 10,
"session_id": "XXXXXXXXXX",
"items": [
{
"item_name": "Top-up"
}
]
}
}]
}
but we are not sending timestamp_micros. And we send 'user_id_dimension' as user property with the same value as 'user_id' parameter to observe user id further in Exploration reports. We've created user-scoped custom dimension in GA4 interface with dimension name User ID and this user property 'user_id_dimension'. Everything works