Play Music on iPad through a Bose Wave Music 4 (not bluetooth!).

I have an iPad mini 6 and a Bose Wave 4 music system. I naively thought that connecting the two with a USB C to 3.5mm cable would work - it didn't. The Bose is not bluetooth and I do not have the Bose bluetooth adaptor. How can I play music from my iPad and hear it through the Bose?

I used to be able to do this with lightning cable, so how can I do it now that I have USB C coming off my iPad and iPhone?

I'd like a solution that isn't going to cost me a fortune!