Magnolia 5.5 reached end of life on November 15, 2019. This branch is no longer supported, see End-of-life policy.
If the author instance tries to publish content to a public instance missing a valid license you will see the following in the log:
info.magnolia.module.exchangetransactional.TransactionalSyndicator – Non EE subscriber detected. info.magnolia.cms.exchange.ExchangeException: Non EE subscriber detected.
To resolve this issue, see the section on updating a key on this page License.