Invoking the scenario with Link scenario step, when you have to wait until linked scenario is completed.
Synch scenarios are several times slower than regular ones plus they consume your app resources with 3x coefficient.
Any scenario can be run synchronically, despite of selected triggers.
Running synch scenarios in POST-requests
In order to run the scenario synchronically with POST-request, you have to pick it in API-endpoint settings.
If API-endpoint has a Sync scenario, all the objects came with POST-requests (including requests from the form) will be processed in this scenario. The respond to the POST request will include the object after being processed in the scenario.
Running scenarios synchronically with Link scenario step
If you link scenario a-synchronically (by default), the object proceeds its way through the scenario. If you call the scenario synchronically, the object waits until the linked scenario is completed.