The issue lies in axios, i didnt know, what axios has sometimes problems using a http Proxys with https:// requests.
A good workaround is found here at github:
https://github.com/axios/axios/issues/4531#issuecomment-1081264893
const axios = require('axios');
const { HttpProxyAgent, HttpsProxyAgent } = require('hpagent')
const httpAgent = new HttpProxyAgent({
proxy: 'proxy url'
})
const httpsAgent = new HttpsProxyAgent({
proxy: 'proxy url'
})
const instance = axios.create({ httpAgent, httpsAgent });
instance.post('http://example.com')