Errors Adding Foreign Keys (MySQL) (Error Code 1215) - mysql

Question

I am trying to add a foreign key between two different sets of tables, the first set is customer and shopping_cart. I tried looking at the other posts regarding this error but I couldn't get it to work after looking at them.
CREATE TABLE `usale`.`customer` (
CREATE TABLE `usale`.`customer` (
`customer_id` SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
`first_name` VARCHAR(45) NOT NULL,
`last_name` VARCHAR(45) NOT NULL,
`email` VARCHAR(50) NULL DEFAULT NULL,
`active` TINYINT(1) NOT NULL DEFAULT TRUE,
`create_date` DATETIME NOT NULL,
`last_update` TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP,
`student_student_id` BIGINT NOT NULL,
`student_school_id` BIGINT NOT NULL,
`shopping_cart_cart_id` TINYINT UNSIGNED NOT NULL,
PRIMARY KEY (`customer_id`, `student_student_id`, `student_school_id`)),
INDEX `fk_customer_student1_idx` (`student_student_id` ASC,`student_school_id` ASC),
INDEX `fk_customer_shopping_cart1_idx` (`shopping_cart_cart_id` ASC),
CONSTRAINT `fk_customer_student1`
FOREIGN KEY (`student_student_id`)
REFERENCES `usale`.`student` (`student_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION,
CONSTRAINT `fk_customer_shopping_cart1`
FOREIGN KEY (`shopping_cart_cart_id`)
REFERENCES `usale`.`shopping_cart` (`cart_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION)
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8;`customer_id` SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
`first_name` VARCHAR(45) NOT NULL,
`last_name` VARCHAR(45) NOT NULL,
`email` VARCHAR(50) NULL DEFAULT NULL,
`active` TINYINT(1) NOT NULL DEFAULT TRUE,
`create_date` DATETIME NOT NULL,
`last_update` TIMESTAMP NULL DEFAULT CURRENT_TIMESTAMP,
`student_student_id` BIGINT NOT NULL,
`student_school_id` BIGINT NOT NULL,
`shopping_cart_cart_id` TINYINT UNSIGNED NOT NULL,
PRIMARY KEY (`customer_id`, `student_student_id`, `student_school_id`))
CREATE TABLE IF NOT EXISTS `frankapp`.`shopping_cart` (
`cart_id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
`last_update` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
`cart_total` DECIMAL(12,2) NULL,
PRIMARY KEY (`cart_id`))
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8;
ALTER TABLE customer ADD CONSTRAINT `fk_customer_shopping_cart1`
FOREIGN KEY (`shopping_cart_cart_id`)
REFERENCES `usale`.`shopping_cart`(`cart_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION
I'm getting the error: "ERROR: Cannot add foreign key constraint
Error Code: 1215"
For the second set of tables they are named shopping_cart and shopping_cart_item
CREATE TABLE IF NOT EXISTS `usale`.`shopping_cart_item` (
`shopping_cart_item_id` BIGINT NOT NULL,
`shopping_cart_cart_id` TINYINT UNSIGNED NOT NULL,
`inventory_item_inventory_item_id` BIGINT UNSIGNED NOT NULL,
`inventory_item_student_id` BIGINT NOT NULL,
`inventory_item_inventory_type` VARCHAR(45) NOT NULL,
`inventory_item_student_student_id` BIGINT NOT NULL,
`inventory_item_student_customer_id` BIGINT NOT NULL,
`inventory_item_student_school_id` BIGINT NOT NULL,
`inventory_item_edition_edition_id` BIGINT UNSIGNED NOT NULL,
`inventory_item_edition_author_id` BIGINT NOT NULL,
PRIMARY KEY (`shopping_cart_item_id`, `shopping_cart_cart_id`, `inventory_item_inventory_item_id`, `inventory_item_student_id`, `inventory_item_inventory_type`, `inventory_item_student_student_id`, `inventory_item_student_customer_id`, `inventory_item_student_school_id`, `inventory_item_edition_edition_id`, `inventory_item_edition_author_id`),
INDEX `fk_shopping_cart_items_shopping_cart1_idx` (`shopping_cart_cart_id` ASC),
INDEX `fk_shopping_cart_item_inventory_item1_idx` (`inventory_item_inventory_item_id` ASC, `inventory_item_student_id` ASC, `inventory_item_inventory_type` ASC, `inventory_item_student_student_id` ASC, `inventory_item_student_customer_id` ASC, `inventory_item_student_school_id` ASC, `inventory_item_edition_edition_id` ASC, `inventory_item_edition_author_id` ASC))
CREATE TABLE IF NOT EXISTS `frankapp`.`shopping_cart` (
`cart_id` BIGINT UNSIGNED NOT NULL AUTO_INCREMENT,
`last_update` TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
`cart_total` DECIMAL(12,2) NULL,
PRIMARY KEY (`cart_id`))
ENGINE = InnoDB
DEFAULT CHARACTER SET = utf8;
ALTER TABLE shopping_cart_item ADD CONSTRAINT `fk_shopping_cart_items_shopping_cart1`
FOREIGN KEY (`shopping_cart_cart_id`)
REFERENCES `usale`.`shopping_cart`(`cart_id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION
Once again I am getting error 1215: "ERROR: Cannot add foreign key constraint
Error Code: 1215"