API: Cannot save statement contains Vietnamese characters via API

[emeralddd]

I have recently tried API of Polygon. All things worked correctly until I found I couldn't update statements containing some special Vietnamese characters (eg: ê, ô, ...).

This is my code:

const { default: axios } = require('axios');
const { sha512 } = require('js-sha512');

const a = async () => {
    const key = "xxx";
    const secret = "yyy";

    const date = Math.floor(new Date().getTime() / 1000);
    const rand = 100000 + Math.floor(Math.random() * 900000);

    const apiSig = sha512(`${rand}/problem.saveStatement?apiKey=${key}&lang=english&legend=ê&problemId=351173&time=${date}#${secret}`);

    const req = await axios.post(`https://polygon.codeforces.com/api/problem.saveStatement?apiKey=${key}&lang=english&legend=${encodeURIComponent('ê')}&problemId=351173&time=${date}&apiSig=${rand}${apiSig}`);

    console.log(req.data);
}
a();

Nodejs 20.11.1
Axios 1.6.8

After I had sent the request, I got the error message: "Incorrect signature". Everything worked normally when I removed all the special Vietnamese characters.

So is it a bug or am I wrong in any step?