From an earlier email from Vasil
We're still digging into the exact details as to why this happens but i have been able to reproduce the issue and also figure out that the workaround seems to be to simply not include the "inventoryItemId" : "Customer1" in the JSON payload. Also, please include "name":"Customer 1 Traffic" instead. Though i'm not sure that part is vital, i haven't tested the combination without it.