1. Negotiate directly with Party A: You can contact Party A directly by telephone, e-mail, WeChat, interview, etc. and ask for billing information, such as Party A's taxpayer identification number, address, telephone number, etc.
2. Check the contract: Generally, the contract contains the basic information of Party A, including name, address and contact information. You can get Party A's billing information by viewing the contract.
3. Inquire about the tax authorities: If you know the taxpayer identification number of Party A, you can inquire about the website of the tax authorities or call them to get their billing information.