In Jira, a user field uses the User Picker (Assignee, Reporter and etc) which allows entering of Jira usernames by search.

For Salesforce, the embedded user (Created By, Case Owner, etc.) in the objects use the Lookup (User) field. It is actually stored in the Object ID (e.g., 00590000001VEHS) of the user in the object records.

To synchronize both field types (User Picker and Lookup (User)) it is required to map the field in Jira with Salesforce <Object ID> (e.g., Owner ID) that appears in the Remote Field field list in the Adding a new Mapping.

Then you need to ensure that both sides push and pull the correct values. For Salesforce, it expects to receive and pass the Object ID and for Jira, it expects to receive and pass the Jira username.

This can be done by clicking on the "Map Values" link in field mapping (refer: Mapping values in Jira to values in Salesforce).

The field mapping should look something like the following image:

The following image is for value translations for outbound mapping:

The following image is for value translations for inbound mapping:

ProTip

Some Jira versions expect a different value of username. This value can be confirmed by creating a temporary field mapping to a Salesforce text field.

If your Salesforce IDs are 15 digits, you will need to convert them to 18 digits.