Vacation trip to China for Sri Lankans. How to apply for the L visa?

We are Singaporeans and we are inviting our sri lankan partners to go on a trip with us, We had prepared a letter from singapore indicating their trip fully sponsor by us, and we will also attached the tour invoice that we had booked for them, their financial information and valid passport more than 6 months validity, so therefore please advise us what other documents are required for their tourist L application.