Using integrations
In general, integration is a type of object similar to expression rules. The Usage configuration in the Connection section makes a difference in how an integration is used.
There is the Queries data option. That integration can be used like any other expression rule because it does not change the state of the other system. Appian might call this integration any number of times.
There is also the Modifies data option. This integration can only be used in specific places, as it modifies the state of the other system. Appian makes sure that this integration is only called once to prevent any duplicate updates or inserts in the other system.
The integration you created is meant to initiate the invoice posting process. You would not want to start that process twice for the same invoice. Make sure that the Modifies data option...