Using Request API for creating tickets

Hi, We have been exploring Request API for creating tickets recently and have some queries about their usage and capability.

Currently, we have integrated Ticket API for creating tickets. These tickets are created with an admin/agent token on behalf of the end users.

Now, we are planning to use Request API for creating tickets (to be created by end users), but the requestor id is the Read-Only field in Create API, as mentioned in the documentation here.
https://developer.zendesk.com/api-reference/ticketing/tickets/ticket-requests/

So, how do we set the requestor id for tickets created via Request API? Is this API supposed to be called with the end user's credentials?

Also, we would want to set the organization id and external id for the ticket. Can we do that in Request Create API?

Thanks.