This message can appear if the IMEI (serial number) has already been booked in brodos.net.
To avoid this error please follow the below method:
1. Add the device as usual to your current cash register including IMEI > but please do not add a contract to this position.
2. Add an additional article to the till (e.g. article-number "Optionen").
3. Now add a contract to this additional article.
By this you avoid the error described above.
By doing so the article position of the device might have a negative margin, while the additional article will have a positive margin > in total the margin therefore should be positive also.