Instead of .*?, you can also use [^<]* It might even be more efficient (due to smaller amount of backtracking), but I'm not sure about that.

if ($request->content =~ m!
   <tr> \s*
      <td[^>]*> \s* <p>Transaction Number:</p> \s* </td> \s*
      <td[^>]*> \s* ([^<]+)                    \s* </td> \s*
   </tr>
!xs) {
  print "\nmatched $1\n";
}
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