Access Control Origin

[merlinstardust]

I am able to post messages through your repo but I continue to get the below message on both my local and staging environments

XMLHttpRequest cannot load https://hooks.slack.com/services/randomtext/randomtext.
A wildcard '*' cannot be used in the 'Access-Control-Allow-Origin' header when the credentials flag is true. 
Origin 'https://localhost:3000' is therefore not allowed access.

[luskin]

I have a similar issue, [Error] Fetch API cannot load https://hooks.slack.com/services/XXXXXXXXXXXXXXX. Request header field Content-Type is not allowed by Access-Control-Allow-Headers.