Add a Custom Report to the Memberships > Reports Screen in Paid Memberships Pro.

my_pmpro_reports_extras.php

<?php
/**
 * Add a Custom Report to the Memberships > Reports Screen in Paid Memberships Pro.
 *
 * For each report, add a line like:
 * global $pmpro_reports;
 * $pmpro_reports['slug'] = 'Title';
 *
 * For each report, also write two functions:
 * pmpro_report_{slug}_widget()   to show up on the report homepage.
 * pmpro_report_{slug}_page()     to show up when users click on the report page widget.
 *
 */

global $pmpro_reports;
$pmpro_reports['sample'] = __('My Sample Report', 'pmpro-reports-extras');

// Sample Report for Metabox
function pmpro_report_sample_widget() {	 ?>
    <span id="pmpro_report_sample" class="pmpro_report-holder">
        <p>Hi! I'm a sample report!</p>
        <?php if ( function_exists( 'pmpro_report_sample_page' ) ) { ?>
    		<p class="pmpro_report-button">
    			<a class="button button-primary" href="<?php echo admin_url( 'admin.php?page=pmpro-reports&report=sample' ); ?>"><?php _e('Details', 'paid-memberships-pro' );?></a>
    		</p>
    	<?php } ?>	
    </span>
    <?php
}

// Sample Report for Individual Report Page
function pmpro_report_sample_page() { ?>
    <h1><?php _e( 'This is a Sample', 'pmpro-reports-extras' ); ?></h2>
    <p>This report demonstrates how to add a custom report to PMPro. Enjoy!.</p>
    <?php
}

This recipe is included in the blog post on "Create Custom Reports for the Memberships > Reports Admin" at Paid Memberships Pro here: https://www.paidmembershipspro.com/create-custom-reports-for-the-memberships-reports-admin/