 <p>It means if you try to serialize/deserialize more than 20 different types you will require a paid license. See the test in the source code <a href="https://github.com/ServiceStack/ServiceStack/blob/master/tests/ServiceStack.WebHost.Endpoints.Tests/LicenseUsageTests.cs#L55" rel="nofollow">here</a>. In this case 20 different types are trying to be deserialized, causing a <code>License Exception</code>.</p> <p>From you description, you should be well within the limit of the free license and not have to worry about hitting any limitations.</p>