父母移民，何時遞I-864? Help needed

父母移民，何時遞I-864?

this is the initial question posted by amyz and I have got the same issue. Please advise if you could. Thanks a lot!

My parents's I-130 have been aproved. I received a financial support processing fee notice for $70. After paying the fee, the instruction says to look for further instruction on the receipt page and return all required documents in the envelop provided. The instruction points to the I-864 form. But the instruction on the I-864 form says to wait for NVC to send me the package (including I-864). So should I wait for NVC to send me I-864, or print it online and it myself? thanks

I paid AOS $70 on its website. from there it is NOT clear if I should download and file I-864 along with a "document cover sheet" (basiscally prove fee is paid), or send back document cover sheet alone, or do nothing and wait for futher instruction about I-864?