What if it is there in the variables which has value taken from file.
so if variable has prod\user, to interpolate i would need to use double quotes in the url, like "${user}:", isn't it.

Still works fine:

use strict;
use warnings;

use URI::Escape;
use Test::More tests => 1;

my $user = 'prod\user';
my $have = uri_escape ("${user}:");
my $want = 'prod%5Cuser%3A';

is $have, $want;
[download]

Why don't you provide an SSCCE?

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