In the centre of Bern, Carole sourced slip (5)
I believe the answer is:
error
'slip' is the definition.
(slip can mean an error or mistake)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for error that I've seen before include "Boob" , "Blunder, slip" , "Blunder or mistake" , "Mistake, lapse" , "heresy" .)