Hi @ShubhamAg2
these are the steps that you need to follow:
* Create a Runtime Action that receives the event from the 3rd party system, transforms it in the payload required by the Adobe Commerce order status update REST API, and calls this endpoint
* Create an Event Provider in App Builder and update its metadata with the event from the 3rd party system
* Create an Event Registration in the Developer Console to get the Runtime Action above activated when the event is received
* Configure the 3rd party system to send events to the event ingress API (it will cause the event to be forwarded to the event provider and the runtime action automatically activated)
* If the 3rd party system is not able to call directly the event ingress API (e.g. because it can not create the needed payload or headers), you'll need to implement an event ingestion webhook
Most of these concerns are addressed by the Commerce Integration Starter Kit https://github.com/adobe/commerce-integration-starter-kit/tree/main/actions/order/external/updated, I'd recommend you to check it.
If you have specific questions about App Builder & the Starter Kit you can reach out to us in the Magento Open Source Slack Channels:
#app-builder-community: https://magentocommeng.slack.com/archives/C04KT43Q75K
#app-builder-starter-kit: https://magentocommeng.slack.com/archives/C0717RYNWTB
Let me know if you have further questions.