node js post request - node.js

Question

Success localhost response
Cannot GET /u/coupons at server
Frontend script for post
<script>
var count = document.getElementById("count");
var len = document.getElementById("length");
var pattern = document.getElementById("pattern");
document.getElementById('coupons-button').onclick = function()
{
if(count.value!=="" && len.value!=="")
{
const genReq = new XMLHttpRequest();
let url = `count=${encodeURI(count.value)}&` +
`len=${encodeURI(len.value)}&` +
`pattern=${encodeURI(pattern.value)}`;
genReq.open('POST',`/u/coupons?${url}`,true);
genReq.send();
genReq.onreadystatechange = e => {
if(genReq.readyState === 4 && genReq.status === 200){
let gen = JSON.parse(genReq.response);
if (gen.state === "SUCCESS")
{
var coupons = gen.coupons;
for(var i=0;i<coupons.length;i++)
{
var div = document.createElement('div');
var text = document.createTextNode(coupons[i]);
div.appendChild(text);
document.getElementById('coupons-check').appendChild(div);
}
} else {
var div = document.createElement('div');
var text = document.createTextNode("FAIL TO GENERATE");
div.appendChild(text);
document.getElementById('coupons-check').appendChild(div);
}
}
}
}
}
Server script
admin.post( '/u/coupons' ,(req,res)=>{
let params = getParameters(req);
CouponWorker.generateCoupons({
"len":decodeURI(params.len),
"count":decodeURI(params.count),
"pattern":decodeURI(params.pattern)
}).then((_res) =>{
console.log(_res)
if(_res.success === true)
{
res.status(200).json({
"state":"SUCCESS",
"coupons":_res.coupons
});
}
else{
res.status(200).json({"state" : "FAILED"});
}
});
});
CouponWorker
const firebase = require('./Database');
const voucher_codes = require('voucher-code-generator');
exports.generateCoupons = function(params)
{
var len = params.len;
var count = params.count;
var pattern = params.pattern;
//pattern = pattern.replace(/1/g,'#');
const cpn_db = firebase.firebase.database();
var coupons;
return new Promise((resolve,reject)=>{
coupons = voucher_codes.generate({
length:len,
count:count,
prefix:"AMP-",
pattern: '####-####',
charset:"0123456789ABCDEFGHIJKLMNOPQRSTUVXYZ"
});
if(coupons!==null)
{
for(var i =0;i<count;i++)
{
cpn_db.ref('coupons/cid-'+coupons[i]).set({
"addedOn": getDateTime(),
"code" : coupons[i],
"amount" : 20,
"expireDate" : null,
"isActive" : true,
"isDeleted":false
});
}
resolve({
"success":true,
"coupons":coupons
});
}
else
{
resolve({
"success":false
});
}
});
}
Above given snaps shows the same code running on localhost and server,
localhost working fine,giving output and saving data to firbase while server response 404 not found resource.
I can not find the reason of this error.I tried url req on postman and responses are the same as above