Allow custom extension with WPUF

/* This one is for allowing WP for these particular file types*/

add_filter( 'upload_mimes', function ( $mime_types ) {
    $mime_types[ 'vcf' ] = 'image/svg+xml';

    return $mime_types;
} );

/* This is for the WPUF file upload field to accept the custom file type*/

add_filter( 'wpuf_allowed_extensions', 'wpufe_custom_upload_extensions', 100 );

function wpufe_custom_upload_extensions( $extensions ) {
$extensions = array(
            'images' => array(
            'ext' => '',
            'label' => __( 'Images', 'wpuf-pro' )
        ),
        'audio'  => array(
            'ext' => '',
            'label' => __( 'Audio', 'wpuf-pro' )
        ),
        'video'  => array(
            'ext' => '',
            'label' => __( 'Videos', 'wpuf-pro' )
        ),
        'pdf'    => array(
            'ext' => '',
            'label' => __( 'PDF', 'wpuf-pro' )
        ),
        'office' => array(
            'ext' => '',
            'label' => __( 'Office Documents', 'wpuf-pro' )
        ),
        'zip'    => array(
            'ext' => '',
            'label' => __( 'Zip Archives', 'wpuf-pro' )
        ),
        'exe'    => array(
            'ext' => '',
            'label' => __( 'Executable Files', 'wpuf-pro' )
        ),
        'csv'    => array(
            'ext' => '',
            'label' => __( 'CSV', 'wpuf-pro' )
        ),
       'custom' => array(
                'label' => __( 'Custom Extensions', 'wpuf-pro' ),
            'ext' => 'eps,svg,ai'
    )
);

return $extensions;
}

/**
Then visit WP-content/plugins/wpuf-pro/includes/fields/class-field-file.php, line number 139:

then insert the line below:

'custom'    => __('custom', 'wpuf-pro')
**/