Ok, in summary for anyone else finding this: Using a third party form with a munchkin cookie, the munchkin cookie can be passed to Marketo with the lead record to associate the munchkin session. The parameter should be passed to Marketo like this: _mkt_trk = id:AAA-BBB-CCC&token:_mch-example-1531366223094-64745 If it is passing correctly, it will NOT be in the form fill activity log. Some troubleshooting steps: Change the _mkt_trk to _mkto_trk temporarily to see it show up in the activity log and make sure you have the full value passing correctly. We had it passing in URL encoded at one point, so it wasn't working. Don't forget to change it back to _mkt_trk! You can also use the REST API (specifically this call) to query with the cookie value for the lead id to verify it is associating correctly. Or vice-versa, query with the lead id for the cookie values (you'll likely get more than one back as there is one for each device/browser combo). Huge thanks to Sanford Whiteman​ for his help! ... View more