Error when importing WS return package even though I have the original WS package

Hello,

has anyone come across this issue: I received a world server package (not a return package, a standard package) from a client, and I forwarded it to a translator, who gave me back a return package. Even though I unpacked the original package in my Trados Studio 2021 and have it in my list of projects, when I try to unpack the the return package, I get the following message: "The translation package doesn't contain necessary information. The package you are importing may be a return package." I don't understand why Trados is unable to connect the two.

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