MySQL Cannot add foreign key constraint because of ERROR 1215

This is my first table.

CREATE TABLE `raw_orders` (
`row_id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`order_id` VARCHAR(45) COLLATE utf8mb4_unicode_ci NOT NULL,
`order_revenue` FLOAT NOT NULL,
PRIMARY KEY(`row_id`),
KEY(`order_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

This is my second table

CREATE TABLE `formatted_orders` (
`order_id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT,
`client_order_id` VARCHAR(50) COLLATE utf8mb4_general_ci NOT NULL,
`order_revenue` FLOAT NOT NULL,
PRIMARY KEY(`order_id`),
KEY(`client_order_id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

I am trying to add foreign key in formatted_orders linking it to raw_orders by using this

ALTER TABLE formatted_orders ADD FOREIGN KEY (client_order_id) REFERENCES raw_orders(order_id);

But I get this error ERROR (HY000): Cannot add foreign key constraint

via Chebli Mohamed