Error import postgres database

I have a databse dump db.sql.schema I import it using psql -U user dbname < ~/db.sql.schema After import in my DB I see table mytable but not mytable_id_seq.

# \d mytable
        Table mytable
      Column       |     Type     | Collation | Nullable | Default 
-------------------+--------------+-----------+----------+---------
 id                | integer      |           | not null | 
 field1            | integer      |           | not null | 
 field2            | integer      |           | not null | 
 field3            | integer      |           | not null | 

I got the follwong error:

# INSERT INTO mytable (field1, field2, field3) VALUES (1, 1, 1) RETURNING mytable.id;
ERROR:  null value in column "id" violates not-null constraint
DETAIL:  Failing row contains (null, 1, 1, 1).

My postgres version is 10.12 It looks like auto-increment of id doesn't works. Is it a postgres issue or issue with my dump? Is it loo old or too new?