In full (2,6)
'in full' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for at length that I've seen before include "In exhaustive detail, after a long time" , "Finally" , "In great detail" , "verbose types will speak thus" , "For an extended period" .)
(Other definitions for paid that I've seen before include "Remunerated" , "Settled the bill" , "Aggressive, rowdy" , "See 12" , "Forked out" .)