Merge tickets with API

Hi,
I checked and the tickets are not merged yet.
Here’s what I send and what I receive from the API, I guess I’m using the wrong details.

[14-Dec-2010 11:04:21 UTC] {“id”:“2041”,“number”:“4300000010”,“state_id”:5}
[14-Dec-2010 11:04:25 UTC] RESULT: {“error”:“Object already exists!”}

2041 is the id of the child
4300000010 is the number of the parent (not the id)

Here’re the tickets
MariaDB [zammad]> select id,state_id,number from tickets where id=2041 or number=‘4300000010’;
±-----±---------±-----------+
| id | state_id | number |
±-----±---------±-----------+
| 2028 | 4 | 4300000010 |
| 2041 | 2 | 4300000023 |
±-----±---------±-----------+

Am I using the wrong parameters, should I use something different instead of the number.
Thanks for your help,
Federico