Custom fields with key user extensibility: why a field does not appear in the app, form or API

How key user custom fields work

With key user extensibility, custom fields are created in the Custom Fields app. Each field belongs to a business context (for example a sales document header or item). Creating the field is only the first step: the field is available where its usages are enabled.

Typical usages are:

• User interfaces — the field can be added to a Fiori app through adaptation;
• Reports and CDS views — the field is exposed to analytical and data sources;
• Form templates and email templates — the field is available in output;
• APIs / OData services — the field is included in the relevant service.

Why a field is missing

• The usage for the target (UI, form, API) was not enabled for the field.
• The field exists on the source document but no business scenario transfers it to the follow-on document (for example from a sales order to the billing document).
• The form template was not updated to print the field, or an outdated template is assigned.
• The field was created and published in one system but the extension was not transported to the next one.

How to analyse it

1. Trace the path the value must travel: source document → follow-on documents → output or interface.
2. For each step, check that the field exists in the business context and that the required usage is enabled.
3. Check the business scenarios that copy the field between contexts.
4. Confirm that form templates and APIs actually reference the field.

ERP Preflight's Custom Field Flow Doctor reconstructs this lineage from exported extension metadata and reports the exact step where the field is lost. See Output & Extensibility.