How to use order by before group by in SQLite?

I want to combine information from two data table, t1 and t2

t1:

ID TIME_ADD
 1 1620838960308
 2 1620879991077
 3 1620927396290
 

t2:

ID TIME_START    TIME_END      LEVEL
 1 1620837000611 1620840600621 0
 2 1620837000611 1620846000620 1
 3 1620837000611 1620851400622 0
 4 1620837000611 1620879262116 3
 5 1620837000611 1620881062117 2
 6 1620837000611 1620882862117 0
 7 1620923400574 1620923400577 2
 8 1620923400574 1620930600578 1
 ...

therefore, I have the query as following:

SELECT t1.*, t2.LEVEL 
FROM t1 
INNER JOIN t2 
ON t2.TIME_START < t1.TIME_ADD AND t2.TIME_END >= t1.TIME_ADD 
WHERE t1.TIME_ADD >= '1620837000611' AND t1.TIME_ADD <= '1620882862117'
ORDER BY t1.TIME_ADD
GROUP BY t1.TIME_ADD

And expected result to be

ID TIME_ADD      LEVEL
 1 1620838960308 0
 2 1620879991077 2

However, the query above does not work, and it seems to be that I'm using ORDER BY and GROUP BY wrongly. Spent quite some time to try to find out a way, also looking into using INNER JOIN with LIMIT, but without success. So any support here would be highly appreciated.

The ORDER BY clause comes after the GROUP BY clause.

If you want 1 row for each distinct TIME_ADD of t1 with the LEVEL of the row with the min ID of t2, you can do it with HAVING MIN(t2.ID), which is a feature of SQLite (assuming there is no ID in t2 with a 0 value):

SELECT t1.*, t2.LEVEL 
FROM t1 
INNER JOIN t2 
ON t2.TIME_START < t1.TIME_ADD AND t2.TIME_END >= t1.TIME_ADD 
WHERE t1.TIME_ADD >= '1620837000611' AND t1.TIME_ADD <= '1620882862117'
GROUP BY t1.TIME_ADD
HAVING MIN(t2.ID)
ORDER BY t1.TIME_ADD;

See the demo.