Dimethyl coupon?

I can’t identify what you mean by “Dimethyl coupon” from the information provided. Could you clarify which of these you’re looking for?

1) A coupon/discount offer for a product that contains dimethyl (for example, dimethyl fumarate, dimethyl sulfoxide, dimethylamine, etc.)
2) “Dimethyl” in a patent or drug context (e.g., a company name, a drug substance, or a patent term)
3) A “coupon” site or program named “Dimethyl”
4) Something else (tell me the full phrase, product name, or country)

If you share the product name (or the exact wording on the coupon) and your country, I can look up the likely product and explain how coupons/discounts work for it.