MYSQL using IF statement in a trigger to concatenate

Question

I am having some issues with my database rn. In short, I want it so that when adding a row, if certain column with data type enum is equal to one of the choices, then a fixed VARCHAR can be added to the auto increase that is exemplified in the best answer to the question: How to make MySQL table primary key auto increment with some prefix, here is my current try:

CREATE TRIGGER tg_contracts_insert BEFORE INSERT ON contracts
FOR EACH ROW
BEGIN
    IF NEW.dep := 'IT' THEN
        SET NEW.dep :='IT'
    END IF;
    IF NEW.dep := 'Finanzas' THEN
        SET NEW.dep :='FN'
    END IF;
    IF NEW.dep := 'RH' THEN
        SET NEW.dep :='RH'
    END IF;
    IF NEW.dep := 'Mantenimiento' THEN
        SET NEW.dep :='MN'
    END IF;
    IF NEW.dep := 'Cuartos' THEN
        SET NEW.dep :='CT'
    END IF;
    INSERT INTO contracts_seq VALUES (NULL);
    SET NEW.cid = CONCAT(NEW.dep, LPAD(LAST_INSERT_ID(), 5, '0'));
END

dep is the column with enum data type.

But, it says something about syntax, im not sure why (first time using triggers). Is there anything wrong?