Request for Help with 1 Corinthians 9:16-18

I recently read 1 Corinthians 9:16-18:

"Yet when I preach the gospel, I cannot boast, for I am compelled to preach. Woe to me if I do not preach the gospel! If I preach voluntarily, I have a reward; if not voluntarily, I am simply discharging the trust committed to me. What then is my reward? Just this: that in preaching the gospel I may offer it free of charge, and so not make use of my rights in preaching it."

Is Paul saying that his reward is to offer the Gospel free of charge? If so, how is it his reward? Paul did say earlier in the chapter that he would rather die than not have his boast of not using his rights, making it clear that "[offering the Gospel] free of charge" is of value to him (qualifying it as a reward, maybe?). What are his "rights in preaching it"? Material support from the Corinthians? I'd appreciate some help with this if you have anything to offer or if you need to correct me.