See Common Usage Errors which says:

If the verification does not succeed with the default settings, one can do the following:

• Make sure the needed CAs are in the store, maybe use SSL_ca_file or SSL_ca_path to specify a different CA store.
• If the validation fails because the certificate is self-signed and that's what you expect, you can use the SSL_fingerprint option to accept specific leaf certificates by their certificate or pubkey fingerprint.
• If the validation failed because the hostname does not match and you cannot access the host with the name given in the certificate, you can use SSL_verifycn_name to specify the hostname you expect in the certificate.

I understood. I have the Rest client in my perl script, How i can import CA cert files in Perl CA store like the following Mozilla::CA?

The certificate is not Self Signed certificate.

#!/usr/bin/env perl
use strict;
no warnings;
use Win32::Process;
use REST::Client;
use JSON::Parse ':all';
use MIME::Base64;
use Term::ReadKey;
use Data::Dumper;
use MIME::Lite;
use Config::Properties;
use IO::Socket::SSL;
use LWP::UserAgent; 
use HTTP::Request;
use Mozilla::CA;sub 
my $apiurlapplog1 = $baseurl ."/api/v1/users?" . $pagecount1;
my $client = REST::Client->new();
my @responsetext;
my @responsetextall;

run_api_call {
 #start with connecting to Okta and getting the users
 $client->getUseragent()->proxy(['https'], 'http://proxy.abc.com:8080'
+);
  $client->setHost('sso.abc.com');
  $client->setCert("$cert");
  $client->setKey("$certkey");
  #$client-> SSL_ca_file => Mozilla::CA::SSL_ca_file();
  $client->setCa("$certca1");
  $client->setCa("$certca");
 # $client->setTimeout(10);
  $client->addHeader('Authorization',"SSWS $value");
  $client->addHeader('Accept','application/json');
  $client->addHeader('Content-type','application/json');
  $client->GET($_[0]);
}
 print "$apiurlapplog1 . \n";

run_api_call($apiurlapplog1);
  my $responsecode = $client->responseCode() ;
   my $responsecontent = $client->responseContent() ;
  print "Its Responsecode1 : $responsecode  . \n";
  print "ts Responsecontent : $responsecontent . \n";
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