Some billboards really need approval. What you need to prepare are: renderings and copies of business licenses. The catering industry also needs to provide hygiene licenses. After you go, they will give you an application form for advertising, just fill it out. If your billboard is made by an advertising company, you can also ask the advertising company to help you with the approval procedures. Basically, as long as all advertising companies have this service, it is free, and I am advertising.