Strange CSOB Payment Gw response {"resultCode":900,"resultMessage":"Internal error"}

Question

The payment POST request to https://iapi.iplatebnibrana.csob.cz/api/v1.8

{
"merchantId":"A5043fIaNo",
"orderNo":"116",
"dttm":"20210529205317",
"payOperation":"payment",
"payMethod":"card",
"totalAmount":79,
"currency":"CZK",
"closePayment":true,
"returnUrl":{},
"returnMethod":"POST",
"cart":[
{"name":"Mezisou\u010det:","quantity":1,"amount":70,"description":""},
{"name":"Table Rate (Table Ra","quantity":1,"amount":9,"description":""}
],
"merchantData":"eyJvcmRlcklkIjoiMTE2IiwiY3VzdG9tZXJJZCI6IjIiLCJwYXltZW50IjoiY3NvYiIsInNlc3Npb250b2tlbiI6ImMyNTU5ZGJkZmFhZWZmMTAxOThiODQ1ODBjOWIxZDliNWM3ODNkZTU5ZWEwN2U2MWE3OTNhNjNkMzE3YWYzMTMifQ==",
"customerId":"2",
"language":"CZ",
"ttlSec":1800,
"signature":"jgjrvzL\/RifjtDcqFk8RFOeksg+zExfOgy0KQ8qfFYgoU01Qu7pVdaN3u6RPOc8r2gbusfHoaXns7FOTdufXF4Xe0wOLBt86d2wTI2+SRmip2oX0XRSP4l+cpOqdEUbadl5nNDfIjg\/lVKGExlWpqgEkA\/HBjjioUYcz9z77Ax\/zl+DKQAfqlFas64ttskUjN5+n5ZzzSWY8Rs+k2z3h5JHxuJkV9XKyj6FOzDOSPWa8OuZfqDm4d6BIY2VAl1Jt2gyx4wPbNSCcNRmUnJcx5G2DhFImPRWWEFhjjgNw7+7WJKae+KizVPQbvXFYZygqHoHFlYVeLYYrlm768zwPgQ=="
}

Gives strange not so documented Error response. See Official Wiki

{"resultCode":900,"resultMessage":"Internal error"} 

With http return code 500

What is wrong ?

Answer 1

The payment gateway does not know where to go back after payment card use.

You must fill the returnUrl field in payment request

"returnUrl": "https://put.shop.url.to.process.payment.response.here",

to enter payment gateway.