Is the offer "Pay 200 Saudi Riyals and get petrol vouchers worth 210 Saudi Riyals and a free car wash" halal or haram?

It is permissible to sell gasoline vouchers that include a car wash for the stated value, because the sale is for the quantity of gasoline specified in the vouchers along with the car wash, and there is no gharar (uncertainty), riba (interest), or jahalah (ignorance) involved in that.