Set the amount of a Direct Stripe button based on a variable available on page load

ds-filter-params-amount.php

<?php
/*
* The 'ds_filter_params' filter hook is available since Direct Stripe 2.1.8
*
* We want to set the amount based on a query parameter sent on the previous page, (or any variable available on page load)
* We called the query variable ds_amount
*/
add_filter( 'ds_filter_params', function( $params ){

    if( $params['button_id'] === 'MyButtonID' ) { //EDIT 'MyButtonID' with your own CSS Button ID

        $new_amount = isset($_GET['ds_amount']) ? $_GET['ds_amount']: '';

        if( !empty( $new_amount )) {

            //Set amount to charge
            $params['amount'] = base64_encode( $new_amount );

            //Set amount to display in the Strioe modal form (In case the option Display amount is enabled)
            if( strpos( $new_amount , ',') !== false ) {
                $new_amount = str_replace(',', '.', $new_amount );
            }
            if( is_numeric( $new_amount ) ){
                $params['original_amount'] = $new_amount * 100;
            } else {
                $params['original_amount'] = 0;
            }
        }
    }
    return $params;
} );