Here's a normal GET request made by fetch in WebKit:

GET /v4/getannouncement.sjs HTTP/1.1
Host: api.stibarc.com
Accept-Encoding: deflate, gzip, br
Origin: https://stibarc.com
Referer: https://stibarc.com/
Accept: */*
Sec-Fetch-Dest: empty
Sec-Fetch-Mode: cors
Sec-Fetch-Site: same-site
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/605.1.15 (KHTML, like Gecko)
Accept-Language: en-US