查询visa status -- NVC case问题

按照官网说的，在https://ceac.state.gov/IV 上查，但是需要16 digit Invoice ID for case status -- 这个我没有印象。请问在哪里找？
还是有可能是processing on paper的？




“If you case is processing electronically, please log into your CEAC account at ceac.state.gov/iv with your NVC case number and 16 digit Invoice ID for case status and to learn what steps you must take to advance your case. Disregard the instructions below, they do not apply to electronic processing.

If your case is processing on paper (you mailed paper documents to NVC for review), then the case status and instructions below apply to your case.

Please follow the instructions you received from the National Visa Center (NVC) that list the six steps you must take before NVC can schedule your visa interview appointment. This includes submitting to NVC various fees, forms and documents. Once NVC has received all the required items, they will let you know if anything is missing or incomplete. You can also find these instructions online at http://nvc.state.gov (English) and http://nvc.state.gov/espanol (Spanish). You will find contact information for NVC at http://nvc.state.gov/ask.”

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