UPDATE from CTE syntax error

Good evening,

I am struggling with the syntax, please help.

This query with a CTE works ok:

WITH

extract_letters AS (

SELECT

mid,

STRING_AGG(x->>'letter', '') AS
letters
FROM (

SELECT

mid,

JSONB_ARRAY_ELEMENTS(tiles) AS x

FROM words_moves

WHERE action='play'

) z
GROUP BY mid)

SELECT * from extract_letters;

mid | letters
--------+---------
12 | АКЖОЛ
15 | ДМО
16 | ТО
20 | ШГА
21 | КТИ
22 | ВОЗ
24 | АКПОНК

But UPDATEing from the CTE does not -

WITH extract_letters AS (

SELECT

mid,

STRING_AGG(x->>'letter', '') AS letters

FROM (

SELECT

mid,

JSONB_ARRAY_ELEMENTS(tiles) AS x

FROM words_moves

WHERE action='play'

) z

GROUP BY mid)
UPDATE words_moves m

SET m.letters =
el.letters
FROM
extract_letters el
WHERE
m.mid = el.mid;

ERROR: 42703: column "m" of relation "words_moves" does not exist
LINE 14: SET m.letters = el.letters
^

Regards
Alex