Cant paste litematica on fabric server

When my friend tries to paste a litematica, it says this. Is this bc of fabric or the velocity proxy, or what could be the cause. When trying to paste the structure in he gets kicked and the litematica doesnt paste correctly.
https://media.discordapp.net/attachments/895938137778446386/1124760262772265010/image.png?width=1576&height=62
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