Is it illegal for a restaurant to not accept coupon for discount before expiration?

It is past the expiration date you mention. Are you complaining about something that happened before that date? If so, where did this happen? The location is important because local laws may affect the answer. The only place I have seen use of the term "meal booking" is in colleges in the United Kingdom. Without knowing the details or location, it is not possible to know what laws might be in effect. However, usually in most cases, such a coupon is not considered a contract offer, but is simply considered a promotion. There would be no obligation to honor the coupon. However, in most places, if a business hands out such coupons as a form of "bait and switch," where they lure in customers to try to sell them something more expensive or less desirable, then this may be a deceptive business practice that should be reported to a local Better Business Bureau, a Chamber of Commerce, and possibly to the Federal Trade Commission.