Get data from a form using post

I have three dropdowns and I can’t get data from two of them using POST, here is my code:

<form action="{url module=ProductManagement action=downloadFilteredImages}" method="post">
<table>
    <tbody>
        <tr>
            <td>
                <select class="form-control selectpicker filter" name="category_id" multiple data-live-search="true">
                    {foreach $suppliers as $supplier}
                        <option value="{$supplier.supplier_id}" {if $value eq $supplier.supplier_id}selected{/if}>{$supplier.supplier_name}</option>
                    {/foreach}
                </select>
            </td>
            <td>
                <select class="form-control selectpicker filter" name="category_id" multiple data-live-search="true">
                    <option value="0" selected>{t}Category filter{/t}</option>
                    {include file="./ProductManagement_filters_category.tpl" categories=$categories}
                </select>
            </td>
            <td>
                <select class="form-control selectpicker filter" name="category_id" multiple data-live-search="true">
                    {foreach $order_statuses as $status}
                        <option value="{$status.order_status_id}" {if $value eq $status.order_status_id}selected{/if}>{$status.order_status_name}</option>
                    {/foreach}
                </select>
            </td>
            <td>
                <button type="submit" class="btn btn-primary">
                    {'Download'|t}
                </button>
            </td>
        </tr>
    </tbody>
</table>

I can get the categoryID but not from the supplier or order status

Answer

All three select has same name attribute please change the values name=”category_id”

<select class="form-control selectpicker filter" name="category_id_1" multiple data-live-search="true">
    {foreach $suppliers as $supplier}
        <option value="{$supplier.supplier_id}" {if $value eq $supplier.supplier_id}selected{/if}>{$supplier.supplier_name}</option>
    {/foreach}
</select>
</td>
<td>
<select class="form-control selectpicker filter" name="category_id_2" multiple data-live-search="true">
    <option value="0" selected>{t}Category filter{/t}</option>
    {include file="./ProductManagement_filters_category.tpl" categories=$categories}
</select>
</td>
<td>
<select class="form-control selectpicker filter" name="category_id_3" multiple data-live-search="true">
    {foreach $order_statuses as $status}
        <option value="{$status.order_status_id}" {if $value eq $status.order_status_id}selected{/if}>{$status.order_status_name}</option>
    {/foreach}
</select>