When the field “page_builder: does not exist you need to create it.
$value = array(
// nested array for each row you want to create
array(
// field key => value pairs for row
'acf_fc_layout' => 'one_column',
'field_60745782d2943' => get_the_content();
)
)
update_field('field_key_of_flex_field', $value, $post_id)
