Magento 2 custom ui_grid filterSearch issue

Question

I have an error when attempting to search for a keyword in my custom table

In Network tab, i have a call to

https://mylocalsite.local/admin/mui/index/render/?namespace=my_grid&search=123&filters%5Bplaceholder%5D=true&paging%5BpageSize%5D=20&paging%5Bcurrent%5D=1&sorting%5Bfield%5D=po_date&sorting%5Bdirection%5D=asc&isAjax=true

which returns

{"error":"UI component could not be rendered because of system exception","errorcode":"42"}

And in the exception.log i have:

main.CRITICAL: SQLSTATE[42S22]: Column not found: 1054 Unknown column 'fulltext' in 'where clause', query was: SELECT COUNT(*) FROM purchase_order AS main_table INNER JOIN admin_user AS u ON u.user_id = main_table.created_by WHERE (((fulltext = 'abc')))

In my grid XML declaration i have the following:

...
<dataSource name="my_grid_data_source">
    <argument name="dataProvider" xsi:type="configurableObject">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="update_url" xsi:type="url" path="mui/index/render"/>
                <item name="storageConfig" xsi:type="array">
                    <item name="indexField" xsi:type="string">id</item>
                </item>
            </item>
        </argument>
        <argument name="class" xsi:type="string">Vendor\Module\Ui\DataProvider\Module\GridDataProvider</argument>
        <argument name="name" xsi:type="string">my_grid_data_source</argument>
        <argument name="primaryFieldName" xsi:type="string">id</argument>
        <argument name="requestFieldName" xsi:type="string">id</argument>
    </argument>
    <argument name="data" xsi:type="array">
        <item name="js_config" xsi:type="array">
            <item name="component" xsi:type="string">Magento_Ui/js/grid/provider</item>
        </item>
    </argument>
</dataSource>
...

<listingToolbar>
    ...
    <filterSearch name="fulltext"></filterSearch>
    ...
</listingToolbar>

I have the database indexes in place (created from the install script)

However, when i try to search for something, i am getting that error i posted in the beginning of this question. What am i missing? Thank you.