Filter blog by multiple categories

On my product detail page I would like to filter out some blog posts by case study, and by segment that matches the product.

I have created a category set called Segments

So my post.html & products.html template have the following

<perch:categories id="segments" set="segments" label="Segments" display-as="checkboxes" suppress="true" divider-before="Choose your segment">
    <perch:category id="catSlug" type="slug" />
    <perch:category id="catTitle" type="text" />
</perch:categories>

I have another set called en-eu which has a category called case-studies

So I currently have them filtering like this

$productsegment = perch_collection('products', [
            'filter' => 'slug',
            'value' => perch_get('s'),
            'category-match' => 'all',
            'category' => 'segments/'.perch_get('cat'),
            'template'   => 'products/_product_segment.html',
        ], true);

        $fullsegmenturl = 'segments/'.$productsegment;

        // Strips out all whitespace
        $stripout = preg_replace('/\s+/', '', $fullsegmenturl);





perch_blog_custom(array(
            'category'       => array("en-eu/case-studies", $stripout),
            'category-match' => 'all',
            'count'      => 3,
            'template'   => 'casestudy_image.html',
            'sort'       => 'postDateTime',
            'sort-order' => 'DESC',
            'blog'       => 'en-eu',
        ));

This works but only if there is one category selected on the product page. I need to get it working if the editor selects multiple categories.

Any ideas?

Thanks