Mistake made with packaging of toy piano (4)
I believe the answer is:
typo
'mistake' is the definition.
(typographical error)
'of toy piano' is the wordplay.
'of' indicates anagramming the letters (the answer comes from or 'of' the letters).
'piano' becomes 'p' (musical abbreviation).
'toy'+'p'='toyp'
'toyp' is an anagram of 'TYPO'.
'made with packaging' is the link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for typo that I've seen before include "Literal - printing mistake" , "Literal error in printed matter, in short" , "What's not right" , "Finger problem" , "Printer's error" .)