I am a USA Citizen and would like to apply for a Business (F) visa in the Chinese consulate in Thailand. Besides a) application (2 copies), b) 2 photos, c) invitation letter issued from Chinese company -- what other documentation is needed?

I have been employed by a company in China for the past 5 years but am going to be working as a freelance service provider. They are hiring not as an employee but as service provider. My current work visa expires and should change to a business visa. I currently live in China as well. Do I need any other documentation to obtain the business visa?

Thank you