Supposed to have put on musical in retirement (8)
I believe the answer is:
putative
'supposed' is the definition.
(synonyms)
'put on musical in retirement' is the wordplay.
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'musical' becomes 'evita' (Andrew Lloyd Webber musical).
'in retirement' shows that the letters should be reversed in order (retire can mean to go back or backwards).
'evita' written backwards gives 'ative'.
'put'+'ative'='PUTATIVE'
'to have' is the link.
(Other definitions for putative that I've seen before include "Supposed - tie up vat (anag)" , "Supposed or reputed" , "Generally considered or reputed to be" , "Supposed, generally considered such" , "Supposed or thought to be" .)