myCRED: User ID as Referral ID

add_filter( 'mycred_affiliate_get_ref_id', 'mycred_pro_user_id_affid', 99, 2 );
function mycred_pro_user_id_affid( $ref_id, $user_id ) {
    return $user_id;
}

add_filter( 'mycred_affiliate_get_user_id', 'mycred_pro_get_user_id_affid', 99, 2 );
function mycred_pro_get_user_id_affid( $user_id, $ref_id ) {
    return absint( $ref_id );
}