Store API - Produkt in Warenkorb legen

Zur Info, so geht es:

                        var result = this.responseText;
                        var jsonResponse = JSON.parse(result);
                        var toke = jsonResponse["token"];
                        let formData = new FormData();

                        formData.append('_csrf_token', 'xxx.xxxx.xxxxxxxxx');
                        formData.append('lineItems[e7b6a5682d2c4027bd93b62ddf8d5c25][quantity]', 1);
                        formData.append('redirectTo', 'frontend.cart.offcanvas');
                        formData.append('lineItems[e7b6a5682d2c4027bd93b62ddf8d5c25][id]', 'e7b6a5682d2c4027bd93b62ddf8d5c25');
                        formData.append('lineItems[e7b6a5682d2c4027bd93b62ddf8d5c25][type]', 'product');
                        formData.append('lineItems[e7b6a5682d2c4027bd93b62ddf8d5c25][referencedId]', 'e7b6a5682d2c4027bd93b62ddf8d5c25');
                        formData.append('lineItems[e7b6a5682d2c4027bd93b62ddf8d5c25][stackable]', 1);
                        formData.append('lineItems[e7b6a5682d2c4027bd93b62ddf8d5c25][removable]', 1);
                        formData.append('product-name', 'Werkszeugnis 2.2/3.1');
                        formData.append('brand-name', '');
                        

                        const xhr = new XMLHttpRequest();
                        xhr.withCredentials = true;

                        xhr.addEventListener('readystatechange', function () {
                          if (this.readyState === this.DONE) {
                            // console.log(this.responseText);
                            
                          } else {
                           // console.log(this.responseText);
                          }
                        });

                        xhr.open('POST', 'https://domain.shop/en/checkout/line-item/add');
                        // xhr.setRequestHeader('Content-Type', 'multipart/form-data');
                        // xhr.setRequestHeader('Accept', '*/*');
                        xhr.setRequestHeader('sw-access-key', 'xxxxx');
                        xhr.setRequestHeader('sw-context-token', toke);
                        xhr.send(formData);