If you want to make more than one booking with the same coupon number, you have to enable the checkbox Allow duplicates.
You will have to upload the same coupon file for all the number of bookings allowed with the same coupon. For example, if customers can make 3 bookings with the same coupon number, upload the same coupon file 3 times.
Once you have completed the settings for your promotion, click Save, open the promotion again and you will be able to upload the same coupon file again, by clicking on the Manage button.
More information on Multiple Coupon Codes Promotions Settings.