Sip trunk issue

Just wanted to mention something that happened yesterday on an installation.
Installed latest stable, 10.13.66
Created a sip trunk to a known service provider. Outbound calls would not go. Provider was getting the telephone number followed by @trunkname.
Went into CLI and confirmed that is what the system was sending. Could not find a problem or solution. Finally duplicated the trunk, removed the original trunk, and changed outbound route to use the new duplicate trunk. All worked. Not sure what or why.