How to create custom approval process and invoke using VBS extension

Summary:
I have a requirement where we are creating some custom pages for some transactions using the VBS extension and the client wants to invoke a custom workflow based on BU.

1. Can we create a custom workflow and expose the same as REST API?
2. How to trigger the same using VBS in case there is no REST as VBS is tightly integrated with Fusion HCM.

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