Try to add user agent:

fetch(url, {
    headers: {
        'Authorization': `Basic ${encodedString}`,
        'Cache-Control': 'no-cache'
    },
    "User-Agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/81.0.4044.138 Safari/537.36"
})