Debit-card number must be secure (3)

I believe the answer is:

I believe this clue is a double definition.

'debit-card number' is the first definition.
(I've seen this before)

'secure' is the second definition.
(pinning is a kind of securing)

'must be' acts as a link.

(Other definitions for pin that I've seen before include "Sewer's aid" , "Number allocated for electronic transactions" , "Fixing device" , "Debit-card number" , "Cashpoint code" .)

I've seen this clue in The Telegraph.

Want a hint initially instead of a full solution? Install my app