For this error, the field in question is not accessible to the user profile in Financial Force for the user whose credentials were used to make the connection within Expensify.
To correct this, go to Setup > Build > expand Create > Object
Then go to Payable Invoice > Custom Fields and Relationships
Select the field listed in the error message
Click View Field Accessibility
Then, find employee profile in the list and select Hidden
Make sure both options for Visible are selected
Once this step has been completed, sync the connection within Expensify by going to Admin > [policy name] > Connections > Sync Now and then attempt to export the report again.