After combining the Ancient Device with an insignia, you get the Ancient Pattern Analyzer. I understand you’ve done this step since you mention this item specifically. Once you have that, you trade it with three (different) Silvertail mobs. There’s no use action (i.e. rightclicking) or combining needed besides this. Once you have traded the Ancient Pattern Analyzer to three Silvertails, you trade it back to Sipius Aban Lux-Wel in the garden and then he should give you the key.
I hope this helps 
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