Pre-Fill Wordpress ACF Repeater Field

pre-fill-acf-repeater.php

<?php

// Pre-fills a repeater field (and its sub-fields) with default values
// - assuming we have a Repeater field with the key "repeater_field_123"
// - with the sub-fields "sub_field_1" and "sub_field_2"

function prefill_repeater( $field ) {
    if ($field['value'] === false) {
        $field['value'] = array(
            array(
                'sub_field_1' => 'My sub field 1 default content',
                'sub_field_2' => 'My sub field 2 default content',
            ),
            array(
                'sub_field_1' => 'And another one',
                'sub_field_2' => 'And yet another one',
            ),
        );
    }
  
    return $field;  
}

add_filter('acf/prepare_field/key=repeater_field_123', 'prefill_repeater');

Thank you so much, this is fantastic. Had to search a long time for a solution that works! But for it to really work for me, I had to check $field[value] against empty(), since a newly instantiated repeater field is probably an empty array.