Most residency visa cases that are pending must upload the missing documents through https://ceac.state.gov/ceac/. However, there are cases, and/or documents, that cannot be digital, so it would be necessary to use the Mail Boxes, Etc. (MBE) courier service.
For example, all Fiancé (K) visas require documents to be printed and sent via courier service. Likewise, birth certificates and court documents for every case must be submitted physically and in original through MBE.
Finally, if when you fill out the DS260 you do not have the Documents window, it is because your case is not electronic and all pending documents must be sent in original through MBE, such as the fiancé visas that we mentioned previously.
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