For GTM option you need to make sure that UTM parameters are transferred in URL (not just in cookies) all over the flow, up to the conversion page.
Please use the UTM Tagging in the campaign settings:
By default these fields will be filled in automatically but you can replace with info by your choice. It is highly recommended to use these tracking tags in campaign settings and not to hardcode them in tracking url.
1. In the campaign settings select the Google Tag Manager option in the Conversion sensors block.
Click “Search Gallery”
Enter “MGID” in the search field
Add a ready-made template to the site workspace.
3. Create a new tag (“Tags” -> “New”) by choosing "MGID Pixel" among the tag types in the "Tag Configuration" section.
4. Enter your MGID Client ID in the "Tag Configuration" section, and then choose the event type "Page View".
5. Select "All Pages in the "Triggering" section.
It's important to activate our sensor on all pages so that visitors may be directed from MGID. Otherwise the conversions will not be counted properly.
6. Save this Tag and begin creating a new tag by choosing "MGID Pixel" among the tag types in the "Tag Configuration" section.
7. Enter your MGID Client ID in the "Tag Configuration" section and then choose event type "Conversion to Action".
8. Specify the conversion category (Lead, Sale, Install) and provide the conversion value (your conversion earnings may be specified as a variable).
9. Select the relevant trigger in the "Triggering" section.This trigger will indicate the previously specified conversion has occurred.
E.g: If your "Conversion to Action" is "New Order", then choose the trigger meaning that a new order has been created and successfully submitted ("New Order", "Thank You Page", etc.).
10. If you want to track more stages of the conversion funnel, you can repeat steps 3-9, you must select a different event type "Conversion to Desire" or "Conversion to Interest".
11. In order to make your tags active online you will need to click on "Submit" -> "Publish" at the top right-hand side of the screen.