How to pre-fill clone fields

Pre-filling a clone field is a bit fiddly because the field name (and key) that appears at render time depends on the clone’s Prefix Field Names setting. When it’s enabled, the rendered field’s name is the clone’s name joined with the cloned field’s name.

Handle both cases inside af/field/prefill_value:

add_filter( 'af/field/prefill_value', function ( $value, $field, $form, $args ) {

    // Only run for the target form.
    if ( $form['key'] !== 'YOUR_FORM_KEY_HERE' ) {
        return $value;
    }

    $clone  = 'YOUR_CLONE_FIELD_NAME_HERE';
    $cloned = 'YOUR_CLONED_FIELD_NAME_HERE';

    // Prefix Field Names ENABLED → the rendered field's name is "<clone>_<cloned>".
    if ( $field['name'] === "{$clone}_{$cloned}" ) {
        return 'Value 1';
    }

    // Prefix Field Names DISABLED → the rendered field's name is just <cloned>.
    if ( $field['name'] === $cloned ) {
        return 'Value 2';
    }

    return $value;

}, 10, 4 );

The same logic applies if you’d rather match on field keys — prefixed keys look like field_abc123_field_def456.

How to pre-fill clone fields

See also