How to fix Syntax Error in DATEDIFF trigger - mysql

Question

Can anyone see what is wrong with this code?
Everything was working fine until I added the trigger to calculate the difference between two dates. First of all I altered the table just incase anyone wondered.
ALTER TABLE bookings
ADD COLUMN TheDuration varchar(10);
Then my triggers are as follows...
DELIMITER //
CREATE TRIGGER check_licence /*This trigger will approve customers with a valid licence */
BEFORE UPDATE ON customers
FOR EACH ROW
BEGIN
SET NEW.Status = CASE WHEN NEW.valid_licence = 'Yes'
THEN 'Approved'
ELSE 'Unapproved' /*So if a Customer has a valid licence, He will be automatically approved. */
/*But if he doesn't he will become unapproved[WORKING]*/
SET NEW.TheDuration = DATEDIFF(NEW.bookings.end_date, NEW.bookings.start_date) -- -- TO CALCULATE DURATION BETWEEN 2 DATES
END;
//
DELIMITER ;
The problem lays within
SET NEW.TheDuration = DATEDIFF(NEW.bookings.end_date, NEW.bookings.start_date) -- -- TO CALCULATE DURATION BETWEEN 2 DATES
As everything was working before I added this.
Same here...
DELIMITER //
CREATE TRIGGER Carperperson /* This Trigger Blocks a customer from renting two cars on the same name twice on one day. */
BEFORE INSERT ON bookings /*E.g. Mr.ABC cannot rent a Ford and a Nissan on the same day. Has to return first car first.[WORKING]*/
FOR EACH ROW
BEGIN
IF EXISTS (
SELECT 1
FROM bookings
WHERE NEW.customer_id = bookings.customer_id
AND ((new.start_date >= bookings.start_date
and new.start_date < bookings.end_date)
or (new.end_date > bookings.start_date
and new.end_date < bookings.end_date))
) THEN
SIGNAL SQLSTATE '45000'
set message_text='You can only book one car per single customer a day!' ; /* This triggers only allows to rent a car for 7 days, not more, not less[WORKING]*/
END IF;
IF ( NEW.end_date > NEW.start_date + INTERVAL 7 DAY ) THEN
SIGNAL SQLSTATE '45000'
SET MESSAGE_TEXT = '7 is the maximum. Please choose an earlier date.'; /*The end_date is more than seven days after start_date*/
END IF;
SET NEW.TheDuration = DATEDIFF(NEW.bookings.end_date, NEW.bookings.start_date) -- -- TO CALCULATE DURATION BETWEEN 2 DATES
END;
//
DELIMITER ;
Problem lays within...
SET NEW.TheDuration = DATEDIFF(NEW.bookings.end_date, NEW.bookings.start_date) -- -- TO CALCULATE DURATION BETWEEN 2 DATES