Merchant outbox has been disabled since 2015 because Linden Labs upgraded to the Viewer-Managed Marketplace.
Singularity Viewer still has a Merchant Outbox feature (which gives error 503 because this service is no longer available in Second Life).
Will Singularity Viewer be receiving the Viewer-Managed Marketplace feature, or do we have to use other viewers to manage our Marketplace Listings?
Daniel, as of this time it appears you will need to use another viewer to manage VMM. I know this was a task that needed to be done in viewer when the Lindens released the feature and, as I am not a developer, have no idea how difficult it is to implement it within Singularity. The last word on the topic I had from one of the main developers was... "a lot."
So, for now, it appears another viewer is needed to manage VMM.
Thanks for the reply Sappadilli!
I've been using Firestorm for VMM, hopefully one day I'll be able to uninstall it and use Singularity for everything!
Thiss is in the nightly