for my $Transaction835 ($xp->find('//Transaction835')->get_nodelist) {
...
    for my $ClaimPaymentInformationLoop ($xp->find('.//ClaimPaymentInformationLoop', $Transaction835)->get_nodelist) {
    ...
        for my $ServicePaymentInformationLoop ($xp->find('.//ServicePaymentInformation', $ClaimPaymentInformationLoop)->get_nodelist) {