PayPal API V2创建订单持续触发MALFORMED_REQUEST_JSON错误求助

问题重现 #

调用PayPal API V2创建订单时，持续收到MALFORMED_REQUEST_JSON格式错误提示。先后两次调整请求JSON结构（替换application_context为payment_source、添加amount的breakdown字段），但错误未解决。

初始请求JSON #

{"intent":"CAPTURE","purchase_units":[{"items":[{"name":"Heartless","description":"Short sleeve tshirt 230gram of 100% cotton, Heartless print on front empty back.","quantity":2,"unit_amount":{"currency_code":"EUR","value":25.0}},{"name":"NASCAR","description":"Short sleeve tshirt 230gram of 100% cotton, NASCAR car print on front empty back.","quantity":1,"unit_amount":{"currency_code":"EUR","value":25.0}}],"amount":{"currency_code":"EUR","value":"75"},"custom_id":65}],"application_context":{"return_url":"https://localhost:3000/order/success","cancel_url":"https://localhost:3000/cancel"}}

修改后的请求JSON #

{"purchase_units":[{"items":[{"name":"Heartless","description":"Short sleeve tshirt 230gram of 100% cotton, Heartless print on front empty back.","quantity":2,"unit_amount":{"currency_code":"EUR","value":25.0}},{"name":"NASCAR","description":"Short sleeve tshirt 230gram of 100% cotton, NASCAR car print on front empty back.","quantity":1,"unit_amount":{"currency_code":"EUR","value":25.0}}],"amount":{"currency_code":"EUR","value":"75","breakdown":{"item_total":{"currency_code":"EUR","value":"75"}}},"custom_id":65}],"intent":"CAPTURE","payment_source":{"paypal":{"experience_context":{"brand_name":"Fimetsu","user_action":"PAY_NOW","return_url":"https://localhost:3000/order/success","cancel_url":"https://localhost:3000/cancel"}}}}

返回错误信息 #

{"status": "success","url": {"name": "INVALID_REQUEST","message": "Request is not well-formed, syntactically incorrect, or violates schema.","debug_id": "94d5cca2ed833","details": [{"location": "body","issue": "MALFORMED_REQUEST_JSON","description": "The request JSON is not well formed."}],"links": [{"href": "https://developer.paypal.com/docs/api/orders/v2/#error-MALFORMED_REQUEST_JSON","rel": "information_link","encType": "application/json"}]}}

调用代码 #

response = requests.post('https://apim.sandbox.paypal.com/v2/checkout/orders', headers=headers, data=data)

其中data的类型为<class 'dict'>

问题根源 #

核心错误在于请求体编码方式不符合API要求：

• 使用requests.post的data参数传入Python字典时，requests会默认将其编码为application/x-www-form-urlencoded格式，而非PayPal API要求的application/json格式。
• PayPal API无法解析表单编码的请求体，因此返回MALFORMED_REQUEST_JSON错误。

解决方案 #

有两种修正方式：

方式1：使用json参数替代data参数 #

requests库的json参数会自动将字典序列化为JSON字符串，并自动设置Content-Type: application/json请求头：

response = requests.post('https://apim.sandbox.paypal.com/v2/checkout/orders', headers=headers, json=data)

方式2：手动序列化并设置请求头 #

如果需要手动控制序列化过程，可使用json.dumps()将字典转为JSON字符串，同时确保请求头包含Content-Type: application/json：

import json

headers['Content-Type'] = 'application/json'
response = requests.post('https://apim.sandbox.paypal.com/v2/checkout/orders', headers=headers, data=json.dumps(data))

额外验证点 #

除编码问题外，可同步确认以下细节避免潜在错误：

• custom_id字段：PayPal API要求该字段为字符串类型，建议将数字65改为字符串"65"。
• 金额字段：确保所有value字段格式统一，可保留数字类型或转为标准字符串格式（如"25.00"）。

内容的提问来源于stack exchange，提问作者david backx