Parameters (note that all parameters, except for campaign_name, are mandatory. However, I highly recommend including campaign_name as well – analyzing campaign effectiveness by ID alone is, to put it mildly, not very convenient):

campaign_id: corresponds to the UTM parameter utm_id. Yes, you read that right. You don't often come across utm_id in standard UTM tagging rules. But this parameter is essential for importing cost data into GA4.
campaign_name: corresponds to the UTM parameter utm_campaign.
source: corresponds to the UTM parameter utm_source.
medium: corresponds to the UTM parameter utm_medium.
date: the date for which you're uploading the data.

Metrics (technically, each metric is optional, but you're likely to want to transmit all of them):

impressions: the number of impressions for the ad campaign on the specified date, represented as an integer.
clicks: the number of clicks for the ad campaign on the specified date, represented as an integer.
cost: the total amount spent on the ad campaign for the specified date, in the format 0,000.00. Note that the decimal separator is a period (.).

In short, to successfully import your data, you'll first need to tag your advertising activities with the necessary parameters and then set up the import itself.

Below is an example of tagging for Facebook. The main idea is that you need to include the required values from the ad platform in the UTM parameters of your URL.

Typically, you'll need to go to the ad level and append the appropriate UTM attributes to the final URL used in the ad. In Facebook, this can be done here:

Comparing traffic sources between GA4 and session_traffic_source_last_click in BigQuery

Step-by-step guide: How to Set Up Automatic Import of Advertising Costs into Google Analytics 4 using Facebook Ads as an example

Comparing traffic sources between GA4 and session_traffic_source_last_click in BigQuery

Step-by-step guide: How to Set Up Automatic Import of Advertising Costs into Google Analytics 4 using Facebook Ads as an example