NET
18 What then is my reward? That when I preach the gospel I may offer the gospel free of charge, and so not make full use of my rights in the gospel.
Darby
18 What is the reward then that I have? That in announcing the glad tidings I make the glad tidings costless [to others], so as not to have made use, as belonging to me, of my right in [announcing] the glad tidings.
KJV
18 What is my reward then? [Verily] that, when I preach the gospel, I may make the gospel of Christ without charge, that I abuse not my power in the gospel.