Crossword Genius

So long, and thanks again (2-2)

Ross

I believe the answer is:

ta-ta

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

'so long' is the definition.
(both are ways of saying goodbye)

'thanks again' is the wordplay.
I cannot quite see how this works, but
'thanks' could be 'ta' (UK informal version of 'thank you') and 'ta' is present in the answer.
The remaining letters 'ta' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...

'and' is the link.

Can you help me to learn more?

(Other definitions for ta-ta that I've seen before include "A Farewell" , "Bye!" , "Adieu" , "Bye-bye" , "Cheerio" .)

I've seen this clue in The Independent.
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