I looked into this issue and found out that it's not a problem with the proxy provider.
I was testing steam-user functionality in Deno, which is not fully compatible with Node.js—especially with https-proxy-agent, which steam-user uses under the hood.
import axios from 'axios';
import { HttpsProxyAgent } from 'https-proxy-agent';
const httpsAgent = new HttpsProxyAgent('PROXY_URL_HERE');
const instance = axios.create({ httpsAgent, timeout: 15000 });
const res = await instance.get('https://steamcommunity.com');
console.log(res.data, res.status);
For instance, this code works perfectly fine in Node.js, whereas in the Deno runtime, it throws an error.
I guess I'll have to stick with Node.js for now.