How can I use Paypal Smart buttons to check out using paypal merchant id (partner id)

I'm working with the PayPal Partner Referral API to onboard merchants for different products. However, I’m encountering an error when trying to request multiple products together in a single

<script        src="https://www.paypal.com/sdk/js?client-id=<?php echo PAYPAL_SANDBOX ? PAYPAL_SANDBOX_CLIENT_ID : PAYPAL_PROD_CLIENT_ID; ?>&disable-funding=credit&currency=<?php echo CURRENCY; ?>&merchant-id=<?=$paypal_merchant_id;?>"></script><script>    document        .getElementById("checkoutForm")        .addEventListener("submit", function(event) {            event.preventDefault();            var form = document.getElementById("checkoutForm");            var totalamount = $('#totalamount').val();            var trans_charges = $('#trans_charges').val();            console.log("Total Amount", totalamount, "Trans charges", trans_charges, "loggedin", loggedin);            // render button            paypal.Buttons({                createOrder: function(data, actions) {                    // Create an order on the client side with the cart details                    return actions.order.create({                        purchase_units: [{                            amount: {                                currency_code: 'USD',                                value: totalamount // Replace with the actual cart total                            },                            payee: {                                email_address: '<?=$paypal_partner_merchant_id;?>' // an email                            },                            payment_instruction: {                                disbursement_mode: 'INSTANT',                                platform_fees: [{                                    amount: {                                        currency_code: 'USD',                                        value: '<?=$site_settin["trans_charges"];?>' // Platform fee                                    },                                    payee: {                                        merchant_id: '<?=$paypal_merchant_id;?>' // an alpha-numeric key from paypal                                    }                                }]                            }                        }]                    });                },                onApprove: function(data, actions) {                    console.log("Data", data);                    // Capture the funds from the transaction                    return actions.order.capture().then(function(details) {                        console.log("Details", details);                    });                },                onError: function(err) {                    console.error('PayPal Button Error:', err);                }            }).render('#checkoutForm');        });</script>

this opens up a paypal popup goes through the complete process

and when I complete the payment it gives me error; .can any one help me thanks