This typically happens when your Intuit QuickBooks/Field Promax token has expired. Follow the below steps to disconnect and reconnect which updates your tokens.
Disconnect from QuickBooks. (You need to be logged in as the main administrator for Field Promax). Go to Settings -> Company.
Logout of Field Promax. Log back into in Field Promax
Connect to QuickBooks by clicking on the green Connect button.
Logout of Field Promax. Log back into in Field Promax
Sync your data by clicking on the Sync button.
