#$bet = "and CONVERT(CHAR(10),tdate,101) between '?' and '?'";

try

my @args;
...

$bet = "and CONVERT(CHAR(10),tdate,101) between ? and ?";
#                                               ^     ^
#                                             not quoted

push @args, $fromdate, $today;
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And then pass @args to the exec_select call.