Exception: Failed to read the file

I am getting this when clicking on PDF Invoice from the wp-admin panel:

Exception: Failed to read the file
#0 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/lib/Cpdf.php(5682): Imagick->__construct('/srv/www/ultimu...')
#1 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/lib/Cpdf.php(5807): Dompdf\Cpdf->addImagePngAlpha('/srv/www/ultimu...', 57.442913385827, 727.75417322835, 452.46178073895, 85.03937007874, 6)
#2 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Adapter/CPDF.php(872): Dompdf\Cpdf->addPngFromFile('/srv/www/ultimu...', 57.442913385827, 727.75417322835, 452.46178073895, 85.03937007874)
#3 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Renderer/Image.php(114): Dompdf\Adapter\CPDF->image('/srv/www/ultimu...', 57.442913385827, 29.096456692913, 452.46178073895, 85.03937007874, 'normal')
#4 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Renderer.php(293): Dompdf\Renderer\Image->render(Object(Dompdf\FrameDecorator\Image))
#5 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Renderer.php(127): Dompdf\Renderer->_render_frame('image', Object(Dompdf\FrameDecorator\Image))
#6 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Renderer.php(194): Dompdf\Renderer->render(Object(Dompdf\FrameDecorator\Image))
#7 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Renderer.php(194): Dompdf\Renderer->render(Object(Dompdf\FrameDecorator\TableCell))
#8 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Renderer.php(194): Dompdf\Renderer->render(Object(Dompdf\FrameDecorator\TableRow))
#9 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Renderer.php(194): Dompdf\Renderer->render(Object(Dompdf\FrameDecorator\TableRowGroup))
#10 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Renderer.php(194): Dompdf\Renderer->render(Object(Dompdf\FrameDecorator\Table))
#11 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/FrameReflower/Page.php(148): Dompdf\Renderer->render(Object(Dompdf\FrameDecorator\Block))
#12 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/FrameDecorator/AbstractFrameDecorator.php(895): Dompdf\FrameReflower\Page->reflow(NULL)
#13 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/vendor/dompdf/dompdf/src/Dompdf.php(838): Dompdf\FrameDecorator\AbstractFrameDecorator->reflow()
#14 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-pdf-maker.php(54): Dompdf\Dompdf->render()
#15 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/includes/documents/abstract-wcpdf-order-document.php(712): WPO\WC\PDF_Invoices\PDF_Maker->output()
#16 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/includes/documents/abstract-wcpdf-order-document.php(747): WPO\WC\PDF_Invoices\Documents\Order_Document->get_pdf()
#17 /srv/www/ultimus.ch/public_html/wp-content/plugins/woocommerce-pdf-invoices-packing-slips/includes/class-wcpdf-main.php(360): WPO\WC\PDF_Invoices\Documents\Order_Document->output_pdf('inline')
#18 /srv/www/ultimus.ch/public_html/wp-includes/class-wp-hook.php(292): WPO\WC\PDF_Invoices\Main->generate_pdf_ajax('')
#19 /srv/www/ultimus.ch/public_html/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters('', Array)
#20 /srv/www/ultimus.ch/public_html/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#21 /srv/www/ultimus.ch/public_html/wp-admin/admin-ajax.php(187): do_action('wp_ajax_generat...')
#22 {main}