Error sending form to save

Question

You are generating the following error by submitting my record form: Notice: Undefined index: client in C: xampp htdocs guaraparivirtual Adm-gc write-text.php on line 3

This code below $idcli = $_GET['cliente']; is the client code I get from another page before I get here. The next code also needs to receive this parameter to save the data to the correct client, and this is where it generates the error, because this parameter is passed by action form.

Form page:

<?php
$idcli = $_GET['cliente'];
?>
<?php
$painel=mysqli_query($con,"select detalhe_sobre from anuncios where id = '$idcli'");
while($painel_texto=mysqli_fetch_array($painel)){
$texto_empresa = $painel_texto['detalhe_sobre'];
}
?>
<form class="frm-adm-painel" action="gravar-texto.php?cliente=<?php echo $idcli; ?>">
    <textarea name="textoempresarial" rows="10" placeholder="Texto sobre a Empresa">
    <?php echo utf8_encode(strip_tags(nl2br($texto_empresa)));  ?>
    </textarea>
    <button type="submit">GRAVAR</button>
</form>

Page that generates the error:

The line that generates the error is this: $idcli = $_GET['cliente'];

<?php
$idcli = $_GET['cliente'];
?>
<?php
if (isset($_POST["submit"])){
    echo "Gravado com sucesso";
}
?>