Was this a typo?

my $signature = getSignatures($privateKey, $binarySecurityToken, $time
++stamp, $content);
 #==here it's getSignatures
print $signature;

####

sub getSignature($$)        #==here it's <b>getSignature</b>
{
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In case it wasn't clear what I meant, the sub is defined as "getSignature($$)", while you called it as "getSignatures" (note the missing s at the end of the function name.
Otherwise, the previous response should get you there :-)