I am trying to e-file a 1040x for 2021. I have reviewed the instructions, but I still get the message that I can't e-file because the original was not e-filed. Why am I getting this message? The file was originally paper because the client owed money. Client mailed all of the documents to IRS; cashed the check then months later stated that all of the documents were not in the package. Client mailed the remainder of the documents that the IRS "stated were not in there". Received another letter  saying more documents were missing. Client is in possession of their copy with all documents. Client called IRS and they told him that he must file an amended return with their numbers and his numbers as e-file. I just can't get it to e-file. How do I accomplish this? Another client had a similar issue - when I spoke with the IRS they stated that they can't explain why documents are missing in their system - especially from prior years.

HELP! Please