Dropdown dependent text field missing on a giving form

Open Online Giving → Campaigns or Online Giving → Forms, select the campaign or form, then go to Giving Experience → Form Builder and select the appropriate Pre-Payment Form or Post-Payment Form.

In the giving form, a dropdown's child field appears for a nonempty choice. Selecting the blank choice hides and clears it. Confirm the child text field was actually added under the intended dropdown, save, and preview each choice. Selecting a field type alone is not proof that its child exists. If the field is still absent, obtain the exact form and failure details rather than diagnosing it from its labels alone.