ajax sending form n works, gives an error in the console as in the screenshot 
btnSubmit.onclick = function(){ // ΠΠΎΠ»ΡΡΠ΅Π½ΠΈΠ΅ ID ΡΠΎΡΠΌΡ var formID = 'price_form'; // ΠΠΎΠ±Π°Π²Π»Π΅Π½ΠΈΠ΅ ΡΠ΅ΡΡΡΠΊΠΈ ΠΊ ΠΈΠΌΠ΅Π½ΠΈ ID var formNm = $('#' + formID); $.ajax({ type: "POST", url: 'assets/snippet/ajax.php', data: formNm.serialize(), success: function (data) { // ΠΡΠ²ΠΎΠ΄ ΡΠ΅ΠΊΡΡΠ° ΡΠ΅Π·ΡΠ»ΡΡΠ°ΡΠ° ΠΎΡΠΏΡΠ°Π²ΠΊΠΈ $('#message').html(data); setTimeout(function(){ $('#message').html(' '); },5000); location.reload(); }, error: function () { // ΠΡΠ²ΠΎΠ΄ ΡΠ΅ΠΊΡΡΠ° ΠΎΡΠΈΠ±ΠΊΠΈ ΠΎΡΠΏΡΠ°Π²ΠΊΠΈ $('#message').html('ΠΡΠΈΠ±ΠΊΠ°'); setTimeout(function(){ $('#message').html(' '); },5000); } }); return false; }; </script> form itself
<form id="price_form" action="" name="price_form"> <input type="hidden" name="id_user" value="3"> <div class="data-left"> <label for="">Π£ΠΊΠ°ΠΆΠΈΡΠ΅ ΡΡΠΌΠΌΡ Π²ΡΠΏΠ»Π°ΡΡ, Π½Π΅ ΠΌΠ΅Π½Π΅Π΅ 20 Π </label> <input type="text" min="20" name="sum_user"> </div> <div class="data-left"> <label for="">ΠΠ°Ρ Π±Π°Π»Π°Π½Ρ:</label> <span class="balance">120 Π </span> </div> <div class="data-left small"> <label for="">Π£ΠΊΠ°ΠΆΠΈΡΠ΅ ΡΡΠ΅Ρ:</label> <input type="text" name="invoice"> </div> <div class="data-left small"> <button type="button" id="btnSubmit" class="btn-submit">ΠΡΠΎΠΈΠ·Π²Π΅ΡΡΠΈ Π²ΡΠΏΠ»Π°ΡΡ</button> </div> </form>