山东威海低金额发票贸促会认证-ccpit invoice

我们公司在山东威海，一个沙特客户要付款了，但是他要求发票做贸促会认证，之前我们从来没办理过这个ccpit invoice，这是他给我们发来的信息:
first pay the 30% by RMB , second will make TT BY USD FOR the rest 70% FROM THE CLIENT BANK ACCOUNT to the factory bank account, third , the ccpit invoice which will issue from the factory will be only equal the 70% which sent by usd not by the whole order amount, means reduce the price of each unite by 30%.

我没看懂他说的这个发票的问题,想问下客户是什么意思呢？该如何办理呢？