The meta field is not supported for orders. However, we need to find a way to achieve this, possibly through a prebuilt custom flow. The Customer’s Order Reference/PO Number is crucial for the majority of our customers.
Currently, we can manually enter these into Sales Orders (SOs). However, once the flow in Phase 2 is automated, there will be no opportunity for manual entry, which would be inefficient anyway. For many of our customers, receiving a shipment without a PO# will result in rejection and/or delayed account payment.
Currently, our integration app does not support syncing Metafields for orders. We can only retrieve data from the Order’s JSON field, not from /metafields.json.
Our order flow is mainly using REST API admin and order.metafields is only available for GraphQL API in Shopify.
https://shopify.dev/docs/api/admin-graphql/2023-10/objects/Order#field-metafield

Modifying the pre-built integration for specific requirements is not supported. At this time, we do not have a confirmed timeline for when this will be supported.
Given this limitation, we suggest considering a custom flow to address our client’s specific business needs.
We cannot utilize order metafields (Order Reference) with our pre-built integration, as it does not support mapping or using order metafields. Alternatively, we can use the notes field to enter the Customer Order Reference. The notes field is available in the order JSON and can be directly mapped to NetSuite.
If we need to map from the Order Reference Metafield itself, customization is required. A user event script can trigger upon sales order creation and query the Order Reference from Shopify to set in the NetSuite PO Number.