Insert works but fails for merge

[yudhi s <learnerdatabase99@xxxxxxxxx>]

Hello,

It's version 15.4 postgres. Where we have an insert working fine, but then a similar insert with the same 'timestamp' value, when trying to be executed through merge , it fails stating "You will need to rewrite or cast the _expression_.". Why so?

Example:-

https://dbfiddle.uk/j5S7br-q

 CREATE TABLE tab1 (
    id varchar(100) ,
    mid INT,
    txn_timestamp TIMESTAMPTZ NOT NULL,
    cre_ts TIMESTAMPTZ NOT NULL
) PARTITION BY RANGE (txn_timestamp);

CREATE TABLE tab1_2024_08_09 PARTITION OF tab1
    FOR VALUES FROM ('2024-08-09 00:00:00') TO ('2024-08-10 00:00:00');

-- Below insert works fine 
INSERT INTO tab1
    (id, mid, txn_timestamp, cre_ts)
VALUES
    ('5efd4c91-ef93-4477-840c-a723ae212d84', 123, '2024-08-09T11:33:49.402585600Z', '2024-08-09T11:33:49.402585600Z');

-- Below merge , which trying to insert similar row but failing 

WITH source_data (id, mid, txn_timestamp, cre_ts) AS (
    VALUES ('5efd4c91-ef93-4477-840c-a723ae212d66', 123, '2024-08-09T11:33:49.402585600Z', '2024-08-09T11:33:49.402585600Z')
)
INSERT INTO tab1 (id, mid, txn_timestamp, cre_ts)
SELECT id, mid, txn_timestamp, cre_ts
FROM source_data
ON CONFLICT (id) DO UPDATE
SET    mid = EXCLUDED.mid,
    txn_timestamp = EXCLUDED.txn_timestamp,
    cre_ts = EXCLUDED.cre_ts;

ERROR: column "txn_timestamp" is of type timestamp with time zone but _expression_ is of type text LINE 24: SELECT id, mid, txn_timestamp, cre_ts ^ HINT: You will need to rewrite or cast the _expression_.