Sync & Save automatically displays the form fields that are available to populate.

The following field types are not available to pre-populate:

• Label
• Attachment (Photo, Signature, Audio, etc.)
• Approval
• System fields (start, recordid, etc.)
• Optional Message section of an Email field. (The Email can be populated).
• Calculation

Beginning in version 1.8.0 fields in Repeating Sections, Tables and Grids can be populated. See here for more information.

Some field types have special format requirements:

• Time and Date Time questions
  Sync & Save can parse a wide variety of date formats, however all time values must be in UTC (GMT). 
• Select One
  The value must be an "Underlying Value" as defined on the form.
• Select Multiple
  The value(s) must be one or more of the "Underlying Value" as defined on the form, separated by a space.
• Score
  The value must be the "Underlying Value" as defined on the form.
• Location
  The value must be the Latitude, Longitude, Altitude, and Accuracy, each separated by a space. The Longitude and Latitude must be in decimal format. For example, 40°44'53.04" North 73°59'6.72" West would be entered as "40.748066 -73.9852 0.0 24.0".