Use a different invoice template based on country

functions.php

<?php

add_filter( 'storeabill_invoice_get_template', function( $template, $invoice ) {
    $country     = $invoice->get_taxable_country();
    $template_id = false;
    
    if ( 'AT' === $country ) {
        $template_id = 320;
    } elseif ( $invoice->is_eu() ) {
        $template_id = 323;
    } elseif ( $invoice->is_third_country() ) {
         $template_id = 325;
    }
    
    if ( $template_id ) {
        if ( $template = sab_get_document_template( $template_id ) ) {
            return $template;
        }
    }
    
    return $template;
}, 10, 2 );