In https://www.zabbix.com/documentation/3.0/manual/api/reference/user/create , the description for "usrgrps" says:
The user groups must have the usrgrp property defined.
This seems to be wrong, as the example below uses usrgrpid instead.
The 4.0 version of this page correctly suggests usrgrpid.
It is suggested to fix this not only for all supported versions like 3.0, but for all versions, as this is a small change.