Field Key

Field key is the permanent internal identifier of a custom field.

Automatic generation

For a new field, Checkout Fields creates a key automatically from the label.

Allowed format

• Lowercase Latin letters.
• Numbers.
• Underscores.
• The key must start with a letter.

Generic examples

• billing_tax_id
• delivery_date
• order_reference

After first save

The field key becomes protected because changing it would point future values and shortcodes to a different storage key.