flex table to devide into partitions

Hello, I have flex table mytable. I want to divide the table into partitions by date (there is time field with type Timestamp in the table). I use the following command:
ALTER TABLE mytable
PARTITION BY ((time)::date) GROUP BY (date_trunc('day', (time)::date)) REORGANIZE;

But I get error: ROLLBACK 5371: User defined function not allowed: MapLookup
Why is that?