Creating multiple indexes impossible

In MySQL Workbench, I created a data model. That model has a table where I set two columns to take unique values. The script part is the following:

bq. CREATE TABLE IF NOT EXISTS `tennisMath`.`Court` (

bq.   `idCourt` INT NOT NULL AUTO_INCREMENT,

bq.   `letterNumber` CHAR(2) NOT NULL,

bq.   `surface` ENUM('grass', 'clay') NOT NULL,

bq.   PRIMARY KEY (`idCourt`),

bq.   UNIQUE INDEX `idCourt_UNIQUE` (`idCourt` ASC) VISIBLE,

bq.   UNIQUE INDEX `letterNumber_UNIQUE` (`letterNumber` ASC) VISIBLE)

bq. ENGINE = InnoDB;

Once I forward-engineer the script, I get the following error message:

ERROR 1064 (42000): You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '

UNIQUE INDEX `letterNumber_UNIQUE` (`letterNumber` ASC) VISIBLE)