Shipping price are not the same when you ship to West Indies or inside French borders. You may need postcode is correct.

check_valid_fr_postcode.js

// https://vicopo.selfbuild.fr/
jQuery(function($){var _host=(location.protocol==="http:"?"http:":"https:")+"//vicopo.selfbuild.fr";var _cache={};var _sort=function(a,b){return a.city-b.city};var _filter=function(){return true};$.extend({vicopoSort:function($sort){_sort=$sort},vicopoFilter:function($filter){_filter=$filter},vicopoPrepare:function($cities){$cities=$cities.filter(_filter);return $cities.sort(_sort)},vicopo:function(_input,_done){_input=_input.trim();return this.getVicopo(/^\d+$/.test(_input)?"code":"city",_input,_done)},codePostal:function(_input,_done){return this.getVicopo("code",_input,_done)},ville:function(_input,_done){return this.getVicopo("city",_input,_done)},getVicopo:function(_name,_input,_done){if(_input.length>1){_input=_input.trim();_cache[_name]=_cache[_name]||{};if(_cache[_name][_input]){_done(_input,$.vicopoPrepare(_cache[_name][_input]||[]),_name)}else{var _data={};_data[_name]=_input;return $.getJSON(_host,_data,function(_answer){_cache[_name][_input]=_answer.cities;_done(_answer.input,$.vicopoPrepare(_answer.cities||[]),_name)})}}else{_done(_input,[],_name)}}});$.fn.extend({vicopoClean:function(){return $(this).each(function(){var _removeList=[];for(var $next=$(this).next();$next.hasClass("vicopo-answer");$next=$next.next()){_removeList.push($next[0])}$(_removeList).remove()})},vicopoTargets:function(){var _targets=[];$(this).each(function(){var $target=$(this);$("[data-vicopo]").each(function(){if($target.is($(this).data("vicopo"))){_targets.push(this)}})});return $(_targets)},vicopoTarget:function(){return $(this).vicopoTargets().first()},getVicopo:function(_method,_done){return $(this).keyup(function(){var $input=$(this);$[_method]($input.val(),function(_input,_cities,_name){if(_input==$input.val()){_done(_cities,_name,_input)}})})},vicopo:function(_done){return $(this).getVicopo("vicopo",_done)},codePostal:function(_done){return $(this).getVicopo("codePostal",_done)},ville:function(_done){return $(this).getVicopo("ville",_done)}});var _fields="input, textarea, select";$(document).on("keyup change",_fields,function(){var $target=$(this);var _input=$target.val();if($target.data("vicopo-value")!==_input){var _$targets=$target.data("vicopo-value",_input).vicopoTargets().each(function(){$(this).hide().vicopoClean()});if(_$targets.length&&_input.length){$.vicopo(_input,function(_check,_cities){if(_check===_input){_$targets.each(function(){var $repeater=$(this).vicopoClean();var _$template=$repeater.clone();_$template.show().removeAttr("data-vicopo");var _$cities=[];$.each(_cities,function(){var $city=_$template.clone();$city.addClass("vicopo-answer");$city.find("[data-vicopo-code-postal]").text(this.code);$city.find("[data-vicopo-ville]").text(this.city);$city.find("[data-vicopo-val-code-postal]").val(this.code);$city.find("[data-vicopo-val-ville]").val(this.city);_$cities.push($city)});$repeater.after(_$cities)})}})}}});$(_fields).trigger("keyup")});

// https://css.comonsoft.com/tutoriels/prestashop-filtrer-codes-postaux-pour-les-dom-tom-pays-france.htm
var IsValidMetropolitanFRPostcode = function(postcode) {
    // Corse
    if(parseInt(Number(postcode)) !== postcode) {
        return false;
    }
    
    // DOM TOM
    if((postcode >= 97100 && postcode <= 97699) || (postcode >= 98400 && postcode <= 98899)){
        return false;
    }
    
    return true;  
}

$(document).ready(function() {
    
    if($('#shipping-postcode').length > 0) {
        $('#shipping-postcode').attr('autocomplete', 'shipping-postcode');
        $('#shipping-city').attr('readonly', 'readonly');
        
        $('#shipping-postcode').codePostal(function (cities) {
            let postcode = $('#shipping-postcode').val();
            if(postcode.length < 3) {
                return false;
            }
            
            // Convert city field to select because One postcode can have multiple cities
            $('#shipping-city')
                .replaceWith('<select id="shipping-city" name="shipping_city" class="form-control"></select>');
            
            if(cities.length > 0 && IsValidMetropolitanFRPostcode(cities[0].code)) {
                $.each(cities, function (i, item) {
                    $('#shipping-city').append($('<option>', { 
                        value: item.code,
                        text : item.city 
                    }));
                });
            } else {
                 alert('Vous devez renseigner un code postal valide de France Métropolitaine');
                 return false;
            }
        });
    }
});