Error creating Foreign Key?

Question

MySQL

I want to create for the table "Hotel rooms" ( rooms) a foreign key to the table "Room size" ( roomsize).
I create through the phpmyadmin admin panel, the generated SQL query looks like this:

ALTER TABLE `rooms` 
ADD CONSTRAINT `room_size` 
FOREIGN KEY (`id_room_size`) 
REFERENCES `hotel`.`roomsize`(`id_room_size`) 
ON DELETE RESTRICT 
ON UPDATE RESTRICT;

As a result, it gives the following error:

How to fix this error?
UPDATE:
I also tried to make a connection like this, but again an error

Answer 1

To start:

select * from rooms where rooms.id_room_size not in (
select id_room_size from hotel.roomsize
)