Stick to fax, if possible (5)

I believe the answer is:

affix

I'm a little stuck... Click here to teach me more about this clue!

'stick' is the definition.
(I've seen this in another clue)

'fax if possible' is the wordplay.
'fax if' can be anagrammed to 'AFFIX'.
However, I'm unsure how the anagram is indicated.

'to' is the link.

Can you help me to learn more?

(Other definitions for affix that I've seen before include "Glue" , "Join" , "Attach" , "Append" , "Stick on" .)

I've seen this clue in the Evening Standard.

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