Insist, by the way, that I turned up behind time (9)
I believe the answer is:
stipulate
'insist' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their base form.
Perhaps there's a link between them I don't understand?
'by the way that i turned up behind time' is the wordplay.
'by the way' becomes 'st' (I've seen this in other clues).
'that i' becomes 'upi' (I am not sure about this - if you are sure you should believe this answer much more).
'turned up' shows that the letters should be reversed in order.
'behind time' becomes 'late' (I've seen this in another clue).
'upi' written backwards gives 'ipu'.
'st'+'ipu'+'late'='STIPULATE'
Can you help me to learn more?
(Other definitions for stipulate that I've seen before include "Demand as part of agreement" , "Insist on as part of agreement" , "Make a demand" , "Specify as an essential part" , "Demand, specify" .)