Seeing header but not rows

type Subject = {
    _id: String
    subject: String
    what: {
        description: String
        subtopics: []}
    why: {
        description: String
        subtopics: []}
    how: {
        description: String
        subtopics: []}
}

const columns = [
    {
      header: 'Subject',
      accessorKey: 'subject',
    },
]

function Table(data:Subject[]) {
    const table = useReactTable({
        data,
        columns,
        getCoreRowModel: getCoreRowModel(),
    }) 
    console.log ("mark")
    console.log (data)

    return (
        <table>
            <thead>
            {table.getHeaderGroups().map(headerGroup => (
                <tr
                key={headerGroup.id}>
                {headerGroup.headers.map(header => (
                    <th key={header.id}>
                        {header.isPlaceholder
                            ? null
                            : flexRender(
                                header.column.columnDef.header,
                                header.getContext()
                            )}
                    </th>
                ))}
                </tr>
            ))}
            </thead>
            <tbody>
            {table.getRowModel().rows.map(row => (
                <tr key={row.id}>
                {row.getVisibleCells().map(cell => (
                    <td key={cell.id}>
                    {flexRender(cell.column.columnDef.cell, cell.getContext())}
                    </td>
                ))}
                </tr>
            ))}
            </tbody>
        </table>
    )
}