Anny API doesn't work

We use the anny booking system with API to NUKi. After the booking process, anny reports successful transmission of the request to NUKi and a successful response from NUKi that the request has been received. (Two green check marks). The customer receives an email from NUKi asking him to accept the invitation within 48 hours. He clicks on ‘Accept invitation’ and then sees the code with the orange tick (see screenshot). When he clicks on the tick, he receive a message that the device has already been added. But when he tries to open the door, he receives a message he does not have access. Why? What is going wrong here?