Build a custom AL API page in Dynamics 365 Business Central to expose production order header and line data over OData v4 for an external MES integration

Steps

1. Create an AL extension; define a page of type API with properties APIPublisher, APIGroup (e.g., 'manufacturing'), APIVersion ('v1.0'), EntityName, and EntitySetName pointing to the Production Order table (Table 5405).
2. Add fields from the Production Order table (No., Description, Status, Source No., Quantity, Due Date) as part properties in the page.
3. Define a subpage of type API for production order lines (Table 5406 – Prod. Order Line) and link it via a part with SubPageLink = "Status" = FIELD(Status), "Prod. Order No." = FIELD(No.).
4. Publish the extension to a sandbox environment; the endpoint will be available at /api/<publisher>/<group>/v1.0/companies(<id>)/productionOrders.
5. Secure the endpoint by assigning the API permission set to the integration user; test with a GET request including $expand=productionOrderLines.
6. To allow status changes from the MES, add an OData action (bound function or unbound action via a Codeunit API) to transition the production order status — direct field writes on Status are blocked by business logic.