What’s a good translation of slipped in the following context?
I slipped him a twenty.
I discreetly handed him twenty dollars
Also somewhere between Hannover and Berlin, my take would be "Ich schob ihm 'nen Zwanni rüber", "Zwanni" being common slang for "Zwanziger", the casual word for "Zwanzig-Euro- (oder Mark-) Schein". I like the similarity in cadence and brevity of "twenty" and "Zwanni".
The image evoked by "rüberschieben", move/slide/push over, may be a table; not sure whether "slip" is exactly compatible. But chances are that the exact physical act in the phrase is coincidental anyway.