The error message seems eerily similar to an error message a specific Script Executor will produce if certain functions on their blacklists are called:
I am experiencing this issue with the PromptGamePassPurchase API. Doesn’t happen a lot, but the issue is occurring. I haven’t seen any issues with the PromptProductPurchase API in my experience.
One player who plays my game is consistently having the issue with the error “Attempt to call blocked function PromptProductPurchase on service MarketplaceService”. I can’t reproduce this myself. The user claims that it also doesn’t work if he switches account. The call to the API is made on the client.
Yeah, that’s what I meant. If you check the post I conveniently linked, you will see that the detection works as every script gets affected by the blocklist that I speculate is causing this.