Voice Dream Reader not working on new iPhone 17

I have just started using a new iPhone 17. I have been using the Voice Dream Reader app for a long time, but after transferring everything to this new iPhone, I am encountering an issue. I can still import books, but as soon as I try to play them, the app prompts me about a subscription. I am aware that there were plans for a subscription model, but as far as I know, this was ultimately not implemented. I also purchased the app long before any subscription model was introduced. Is anyone familiar with this issue?