Methods not found

I have this code:
Dim oktaClient = New OktaClient(New OktaClientConfiguration With {
.OktaDomain = oktaConfiguration.OktaDomain,
.Token = oktaConfiguration.Token
})
Dim usersClient = oktaClient.GetUsersClient()

But a get an error, GetUsersClient is not a part of oktaClient. Many samples in internet have this code.

Where is the problem?

Thanks