Divine Vessel fails to activate / didn't work

hey folks

i tried to upgrade my Soul of the Brine King Pantheon today - did Underground Sea with a Divine Vessel, finished it, extracted it from the Map device and talked to Sin. (at this point i didn't know, you can also simply right-click it)

now the Divine Vessel has disappeared from my inventory, the upgrade is NOT unlocked but my map device says 'Activation failed. You have already captured the Soul of this Map's Boss'

any ideas anyone?

nevermind....

stupid people are stupid... Underground Sea != Underground River (and yes - i did 'check' that multiple times...)