I am setting up a server in google app engine and i have linked a custom domain to it also I can access it from the correct URL. I use this server to issue requests to a third party payment gateway where they whitelist the domain of requests.I cant access it because my requests are not coming from the custom domain i linked to the server . I followed this documentation to map the custom domain https://cloud.google.com/appengine/docs/flexible/nodejs/mapping-custom-domains
Is there an additional step to setup outgoing traffic's domain?