Hi Alexey,
REST API documentation will help you,
https://<your soar instance>/docs/rest-api/ui/index.html#/IncidentREST/createIncident.
A small trick;
1- Open developer console on your browser.
2- Listen network traffic, especially fetch/XHR.
3- Open an incident on SOAR
4- Catch the requests that related with opening incident
5- Copy as powershell.

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Burak Karaduman
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