Finally fix digital attachment that's not working (4,4)
I believe the answer is:
nail down
'finally fix' is the definition.
(to nail something down is to settle it for good)
'digital attachment that's not working' is the wordplay.
'digital attachment' becomes 'nail' (nails are attached to toes or fingers, ie digits).
'that's not working' becomes 'down' (down can mean broken or not working).
'nail'+'down'='NAIL DOWN'
(Other definitions for nail down that I've seen before include "Bind to a promise, using hammer and metal pin" , "Identify (something) precisely" , "Firmly fix" , "make final" , "An old win (anag.)" .)