Updating program member custom fields with API.

Hi everyone,

I want to update some program member custom fields of already existing members of the program.

As reported in the documentation, I've already checked the available program member custom fields using this method

https://developers.marketo.com/rest-api/endpoint-reference/lead-database-endpoint-reference/#!/Leads/describeProgramMemberUsingGET

and I got this information 

{
    "requestId": "165da#177dd67a6f1",
    "result": [
        {
            "name": "Program Membership",
            "fields": [
                 .....
                {
                    "name": "Track Name",
                    "displayName": "Nurture Track",
                    "dataType": "string",
                    "length": 255,
                    "updateable": true,
                    "crmManaged": false
                },
                {
                    "name": "Waitlist Priority",
                    "displayName": "Waitlist Priority",
                    "dataType": "integer",
                    "updateable": true,
                    "crmManaged": false
                }
              ]
        }
    ],
    "success": true
}

So as you can see the "Track Name" custom fields is updateable and I tried to update this custom field of an existing membership who belongs to 1111 program, using this method.

https://developers.marketo.com/rest-api/bulk-import/bulk-program-member-import/

and following the example:

curl -i -F format='csv' -F programMemberStatus='Registered' -F file='@example.csv' -F access_token='accesstokenexample' xxxmktorest.com/bulk/v1/program/{programId}/members/import.json

And checking with this url:

xxxmktorest.com/bulk/v1/program/members/export/340e292f-1571-4d6c-ad7a-296a93c394cc/status.json?access_token=accesstokenexample

having this content in the csv file:

Status Reason,Member Date,Status,email,Lead Id,Track Name,Webinar Url
My reason,2019-09-04T19:20:04Z,Registered,myemail@test.com,11122,221133,https://www.testingurl.com/1234

I check the status of the job, and once finished.

https://developers.marketo.com/rest-api/bulk-import/bulk-program-member-import/#polling_job_status

I got this return code:

{"requestId":"c1bf#1773fd05b3d","result":[{"batchId":2366,"importId":"2366","status":"Complete","numOfLeadsProcessed":1,"numOfRowsFailed":0,"numOfRowsWithWarning":0,"message":"Import succeeded, 1 records imported (1 members)"}],"success":true}

As you can see the numberOfRecords parameter is 1, numOfRowsWithWarning is 0 and failed is 0,  however if I check the program member and download all available fields for that member, the Track Name program member custom field is empty along with the other program custom fields I try to update. 

Ex:

Email Address,Track Name
myemail@test.com,,

Is there anything I'm doing wrong or I'm overlooking.??

Thanks a lot for your help!!

David