Signals Notebook: Blacklisted destination URL warning message when creating External Chemical Source

When creating a Chemical External Source you get the warning message "the destination URL is blacklisted. Please choose another destination URL".

Solution: This error could happen due to the URL not resolving to an IP. Also, the URL must be reachable from outside your organization (i.e VPN).  If the URL is valid and reachable from outside your organization and you are still getting this error, please reach out to Support.