Custom code snippet for setting the custom paper size for the client report PDF.

custom-report-pdf-paper-size.php

<?php

// Add the following code snippet to the functions.php file of the MainWP Customisations plugin
// Download MainWP Customisations here: https://github.com/mainwp/mainwp-customisations
// More about the plugin: https://mainwp.com/mainwp-customisations/

add_filter( 'mainwp_client_report_pdf_page_format', 'mycustom_pdf_page_format', 10 , 1 );
function mycustom_pdf_page_format( $format = '' ) {    
    return 'A4';
}