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My solution to the problem is to add reg_number to contact_infos array

$contact_infos = [
            'company' => Configuration::get('PS_SHOP_NAME'),
			'reg_number' => Configuration::get('PS_SHOP_DETAILS'),// added to show Registration Number 
            'address' => [
                'formatted' => AddressFormat::generateAddress($address, array(), '<br />'),
                'address1' => $address->address1,
                'address2' => $address->address2,
                'postcode' => $address->postcode,
                'city' => $address->city,
                'state' => (new State($address->id_state))->name[$this->context->language->id],
                'country' => (new Country($address->id_country))->name[$this->context->language->id],
            ],
            'phone' => Configuration::get('PS_SHOP_PHONE'),
            'fax' => Configuration::get('PS_SHOP_FAX'),
            'email' => Configuration::get('PS_SHOP_EMAIL'),
        ];

and in ps_contactinfo.tpl file you can use $contact_infos.reg_number to show the info