POST API for model with has-many models

We have a simple Sales Order table consisting of a header and one or many line items (obviously this could be any model has-many models object). We can fetch an existing sales order with a simple API call such as:

https://api.domain.com/v1/sales-orders/1

<?xml version="1.0" encoding="UTF-8"?>
<response>
    <id>1</id>
    <code>QTE-200001</code>
    <timestamp>1671926400</timestamp>
    <customer_name>ACME Corporation</customer_name>
    <value>260.00</value>
    <sales_order_items>
        <item>
            <id>1</id>
            <sales_order_id>1</sales_order_id>
            <description>Widget</description>
            <unit_price>90.00</unit_price>
            <quantity>2.00</quantity>
            <line_total>180.00</line_total>
        </item>
        <item>
            <id>2</id>
            <sales_order_id>1</sales_order_id>
            <description>Doodah</description>
            <unit_price>80.00</unit_price>
            <quantity>1.00</quantity>
            <line_total>80.00</line_total>
        </item>
    </sales_order_items>
</response>

The question is, how can we accept and process a POST API request in Yii for a new or existing sales order?