Getting error when trying to make foreign key appear multiple times

Mars has two moons and i want to use its id as a reference for the two moons it has but i get the error above

You have used planet_id twice for one row.
When you INSERT INTO <tablename>() VALUES() you are basically creating a single row in the table.
If you want to create multiple rows in table.
INSERT INTO <tablename>() VALUES (), ();
separate all the value items for row in different paranthesis separated by comma.
INSERT INTO moon(planet_id, name, size, distance_from_nearest_planet) VALUES(3, "name", 22.53, 6000), (4, "name", 22.53, 6000);

oh yeah, thanks. quite a basic error in the end.