Short answers to the questions that break attribution.

GA4 only assigns a default channel when the source and medium match one of its published rules. A medium such as newsletter or fb-ads matches nothing, so the session lands in Unassigned. Stick to recognised mediums like cpc, paid_social, email, referral, affiliate and organic, and keep the platform name in the source.

Pick lowercase, one separator and one word order, then never change them. GA4 treats Spring_Sale, spring-sale and spring_sale as three different campaigns, which quietly splits your reporting. A workable pattern is activity_offer_month, for example winter_sale_july.

Source is where the person came from, such as google, facebook or newsletter. Medium is the marketing method, such as cpc, email or paid_social. Campaign is the activity you want to compare across sources, such as winter_sale_july.

Many sites redirect to a canonical address, strip query strings for caching, or send visitors through a consent or geolocation gateway. If the redirect drops the query string, GA4 records the session as Direct. Our destination check follows the redirects and tells you exactly which parameters survived.

If auto-tagging is enabled, Google Ads appends gclid and populates reporting automatically. Adding manual UTMs on top can override that data. Use manual tagging on Google Ads only when you know why, and keep it consistent across the account.