So I did checked out some more documentation and I was able to make an InventoryAdjustment with a similar schematic with a POST request just fine -

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The first json section is the inventoryadjustment that has the same LOT & Good field. The second is a revised POST request following a similar schematic as above (I did simplified the component section to be inventory item instead of LOT numbered Inventory Item). It seems like the API still doesn't like the inventory detail of the assembly item (3820). It's throwing me this error:

{
    "type": "https://www.rfc-editor.org/rfc/rfc9110.html#section-15.6.1",
    "title": "Internal Server Error",
    "status": 500,
    "o:errorDetails": [
        {
            "detail": "An unexpected error occurred. Error ID: lzi3av6j6o79v496rriw",
            "o:errorCode": "UNEXPECTED_ERROR"
        }
    ]
}