Magnolia 5.6 reached end of life on June 25, 2020. This branch is no longer supported, see End-of-life policy.
If the author instance tries to publish content to a public instance without a valid license, you will see the following in the log:
Non EE subscriber detected.
(When using the Activation and Transactional Activation modules.)
To resolve this issue, see the section on updating a key on the License page.
See also Publishing and activation.