New fixed

only thing that changed is

function buildQuery(site_id, date) {
const query = {
datum: date.format('YYYY-MM-DD'),
kanal: site_id,
callback: 'cb'
}

let c = 4
const a = query.datum + query.kanal + c
const ua = query.kanal + query.datum

let i = a.length,
b = 2

for (let j = 0; j < ua.length; j++) c += ua.charCodeAt(j)
while (i--) {
b += (a.charCodeAt(i) + c * 2) * i
}

b = b.toString()
const key = 'b' + b.charCodeAt(b.length - 1)

query[key] = b

return new URLSearchParams(query).toString()
}