Actually the situation is as follows - at the time of development of the integration, the documentation
https://docs.google.com/document/d/1f_KABuskIAdyFRbTKfQyJO_YchmHy3UPudsC9l3R1-A/... was used, where the key generation method and its transmission in the cid parameter are indicated
Now it turns out that the supplier has changed the API, including the old alternative one to pass the key now in the key parameter (the secret key that you can find on the website, in your personal account, in the API section).
If this is the case (you need to check with them) - then we can finalize the integration / action for a new setting to specify the Key in the final form - this will take 1 hour.