my $numpayments = scalar keys .....
...
if (! --$numpayments) {lastpayments =1}
...
if ( $lastpayments ){ 
    print "last record\n";
};

##</code><code>##

my $numpayments = scalar keys %.....
....
--$numpayments;
...
if(! $numpayments ) {
    print "Last record\n";
}