In [1], the Neutron API checks the validity of the QoS rules before adding them to a policy:

• If a new max-bw rule is lower (max-kbps) than a min-bw rule, the check will fail.
• Same for a min-bw rule, if the min-kbps value is greater than the max-bw rule, the check will fail.

The problem here is that this check doesn't match the rule direction. This can be tested using the following reproducer:
$ openstack network qos policy create qos_test
$ openstack network qos rule create --type bandwidth-limit --max-kbps 2000 --egress qos_test
$ openstack network qos rule create --type minimum-bandwidth --min-kbps 1500 --egress qos_test
$ openstack network qos rule create --type minimum-bandwidth --min-kbps 3000 --ingress qos_test

The latest command will fail despite that the min-bw rule with value 3000 has "ingress" direction and the max-bw rule with value 2000 has "egress" direction.

[1]https://github.com/openstack/neutron/blob/cd26f17e571fd0b62e36662f8494b9a5fd12ae32/neutron/objects/qos/qos_policy_validator.py#L21-L47