Hello , first you don’t have to pay any money when filling out your DS 160. You will pay 265 dollars for visa fee application(roughly 225 pounds).
Furthermore, if there are no schedules you will not be able to pay visa fee, try checking for appointments by 6am , this is when I got mine also it does not mean you will not be able to check other times during the day, the chances are quite high in the morning. Also consular releases date everyday , so don’t worry about not getting appointments , you will soon.
Hope I answered your question.