Summary: Feed submission fails and an error "Error - Unauthorized Request" is returned.
Cause: The host from which you are submitting feeds is not trusted by the search appliance. All hosts submitting feeds must be explicitly permitted in the Admin Console, unless the option Trust feeds from all IP addresses is enabled.
Fix: Explicitly add the host submitting the feeds to the list of trusted hosts in the Admin Console under Crawl and Index > Feeds > List of Trusted IP Addresses or enable Trust feeds from all IP addresses button on the same page.
Additional Information: Trusting feeds from all IP addresses is not recommended for production environments. When this option is selected, any host on the network is able to submit content to the search appliance.