Hey Guys,
I managed to assign a person to 'Assign To' column of the Task in P4TW with Power Automate and Schedule API.
In my scenario I assume that Project, Project Bucket and Bookable Resource already exist and I fetch Bookable Resource record based on email address. I'm creating a new task and then assigning a bookable resource.
The steps are the following:
1: Prepare the data:
Initialize variables
some of variables such as TaskID and TeamID have to be initialized with guid() expression; Other variables in my scenario are hardcoded.

1.1. Get Project Bucket

1.2. Get Project Team

1.3. Get Bookable Resource
<fetch>
<entity name="bookableresource">
<attribute name="userid" />
<attribute name="bookableresourceid" />
<link-entity name="systemuser" from="systemuserid" to="userid">
<filter>
<condition attribute="internalemailaddress" operator="eq" value="@{variables('UserEmail')}" />
</filter>
</link-entity>
</entity>
</fetch>
2. Create Operation Set
Use Perform an unboand action

3. Prepare And Execute Operation Set
Create Team Member
Use action msdyn_CreateTeamMemberV1 from dataverse (perform an unboand action)

{
"TeamMember": {
"@{outputs('OData')}": "Microsoft.Dynamics.CRM.msdyn_projectteam",
"msdyn_projectteamid": "@{variables('TeamID')}",
"msdyn_project@odata.bind": "/msdyn_projects(@{variables('ProjectID')})",
"msdyn_bookableresourceid@odata.bind": "/bookableresources(@{outputs('Get_ResourceID')})"
}
}
Create a Task
Perform an unboand action
{
"@{outputs('OData')}": "Microsoft.Dynamics.CRM.msdyn_projecttask",
"msdyn_projecttaskid": "@{variables('TaskID')}",
"msdyn_project@odata.bind": "/msdyn_projects(@{variables('ProjectID')})",
"msdyn_description": "Test",
"msdyn_subject": "Test resource Assigmnent",
"msdyn_projectbucket@odata.bind": "/msdyn_projectbuckets(@{outputs('Get_Bucket_ID')})",
"msdyn_start": "@{addDays(utcNow(), 1)}",
"msdyn_scheduledstart": "@{utcNow()}",
"msdyn_scheduledend": "@{addDays(utcNow(), 5)}"
}
Create Resource Assignment
Perform an unboand action

{
"msdyn_name": "Test",
"msdyn_projectid@odata.bind": "/msdyn_projects(@{variables('ProjectID')})",
"msdyn_projectteamid@odata.bind": "/msdyn_projectteams(@{variables('TeamID')})",
"msdyn_taskid@odata.bind": "/msdyn_projecttasks(@{variables('TaskID')})",
"@{outputs('OData')}": "Microsoft.Dynamics.CRM.msdyn_resourceassignment"
}
4. Execute Operation Set

And we are done :) Now the new task is created and user is assigned.