add_filter('um_account_page_default_tabs_hook', 'my_custom_tab_in_um', 100 );
function my_custom_tab_in_um( $tabs ) {
    $tabs[800]['mytab']['icon'] = 'um-faicon-pencil';
    $tabs[800]['mytab']['title'] = 'My Custom Tab';
    $tabs[800]['mytab']['custom'] = true;
    return $tabs;
}

/* make our new tab hookable */

add_action('um_account_tab__mytab', 'um_account_tab__mytab');
function um_account_tab__mytab( $info ) {
    global $ultimatemember;
    extract( $info );

    $output = $ultimatemember->account->get_tab_output('mytab');
    if ( $output ) { echo $output; }
}

/* Finally we add some content in the tab */

add_filter('um_account_content_hook_mytab', 'um_account_content_hook_mytab');
function um_account_content_hook_mytab( $output ){
    ob_start();

    echo do_shortcode( '[infusionsoft_invoices]' );

    $output .= ob_get_contents();
    ob_end_clean();
    return $output;
}