GSuite Admin SDK-获取orgUnitPath的所有用户

I'm attempting to get all the users for a particular orgUnitPath. I've set up the org unit for Engineering but currently left it empty (to test that).

Using Go I have the following:

func ListMembers(adm *admin.Service, customerId, orgUnitPath string) ([]*admin.User, error) {
    adm *admin.Service
    return adm.Users.List().Customer(customerId).Fields(googleapi.Field("orgUnitPath=" + orgUnitPath)).Do()
}

A call with my customerId and '/Engineering' gives me the following response:

googleapi: Error 400: Invalid field selection orgUnitPath=/Engineering, invalidParameter

I also tried adding .Projection("full") but get the same error.

I feel like I'm missing something pretty basic here. Any ideas?