Because GA4 has fixed rules for utm_source and utm_medium, if your parameters does not follow the specific format, they will display as “Unassigned”.

The following is the solution how to correctly use UTM parameters in order to match the default format when visitors come.

• utm_source：
  • Set the social media which can be recognized by Google as your UTM parameters such as facebook, instagram, and “Session default channel group” will display “Organic Social”.
  • Set the shopping sites which can be recognized by Google as your UTM parameters such as amazon, ebay (Google currently cannot recognize Shopee), and “Session default channel group” will display “Organic Shopping”.
  • Set the video sites which can be recognized by Google as your UTM parameters such as youtube, twitch, and “Session default channel group” will display “Organic Video”.
  • Set the search engines which can be recognized by Google as your UTM parameters, and “Session default channel group” will display “Organic Search”.
  • Besides the above setting can be used, you also can use one of the following format as your UTM parameters’ settings:
    • The parameters are only written “direct” and cannot include utm_medium. “Session default channel group” will display “Direct”.
    • The parameters are only written “email / e-mail / e_mail / e mail” and cannot include utm_medium. “Session default channel group” will display “Email”.
    • The parameters are only written “sms”.“Session default channel group” will display “SMS”.
    • The parameters are only written “firebase”. “Session default channel group” will display “Mobile Push Notifications”.
• utm_medium：
  • You can use one of the following format as your UTM parameters’ settings:
    • The parameters are only written “social / social-network / social-media / sm / social network / social media”, and “Session default channel group” will display “Organic Social”.
    • The parameters start with “ppc / retargeting / paid” or include “cp”. They will be determined based on utm_source. When you use “Paid Social” as your parameter, “Session default channel group” will display “Paid”
    • The parameters are only written “organic”, and “Session default channel group” will display “Organic Search”.
    • The parameters are only written “email / e-mail / e_mail / e mail”, and “Session default channel group”will display “Email”.
    • The parameters are only written “referral”, ”app”, ”link”, and “Session default channel group” will display “Referral”.
    • The parameters are only written “display”,”banner”,”expandable”,”interstitial”, “cpm”, and “Session default channel group” will display “Display”.
    • The parameters are only written “affiliate”, and “Session default channel group” will display “Affiliates”.
    • The parameters are only written “audio”, and “Session default channel group” will display “Audio”.
    • The parameters are only written “sms”, and “Session default channel group” will display “SMS”.
    • The parameters end with “push” or include “mobile / notification”, and “Session default channel group” will display “Mobile Push Notifications”

Currently, PicSee already written the rule into built-in UTM Builder, and will check your parameters automatically when you enter UTM parameters. When you enter “utm_medium” which does not match the type rule, the website will pop up the warning window. You can go this page to search again.

Lastly, GA4 recommends that custom UTM parameters should use lowercase alphanumerics, dashes (-), underscores (_) or spaces. It is not recommended to use uppercase, Chinese or other symbols.
The above information refers to Google official documentation.