US showman gets cattle invoice (7,4)
I believe the answer is:
buffalo bill
'us showman' is the definition.
(I've seen this before)
'cattle invoice' is the wordplay.
'cattle' becomes 'buffalo' (I have seen 'Wild cattle ' mean 'buffalo' so perhaps 'cattle' could also mean 'buffalo').
'invoice' becomes 'bill' (synonyms).
'buffalo'+'bill'='BUFFALO BILL'
'gets' acts as a link.
(Other definitions for buffalo bill that I've seen before include "travelling showman" , "US showman" , "showman from the West" , "William Frederick Cody, d. 1917" .)