If you have a verbal agreement to get paid especially one with an assistant coach (which has also been reported by Pete Thamel), you didn't have an agreement with the people who actually pay the money.
Sluka committed in January to UNLV. NIL deals can legally get papered, he had months to get it papered and apparently it is only now a huge concern. Maybe it's due to their hot start, maybe someone got in his ear about transferring. I don't know.
Like I feel for dudes who get promised shit and not paid, but welcome to being adult. If you don't have it in writing, you don't have it.