Up to the point where the payments to be reversed get
created via the native Sandbox API, instead of the add-incoming
API, that got recently removed from the Nexus implementation.
Arriving to the point where Libeufin services get
launched and configured with multiple users. The
configuration provides: bank accounts, bank connections
and facades; all being created via the abstraction
"bundling" layer of one Libeufin 'user'.
