ipod touch 7 gen not compatible with homepod mini

Hi, just had to return a new mini homepod I bought last week as I can’t use my iPod touch with it. Basically after latest updates my iPod is on 15.7 and the speaker is on 16.2. I get an error message when I try to connect via AirPlay ( I have 2 iPods both 7 gen, one bought only last April). Went to the Genius Bar today and they couldn’t find a solution, wondering if anyone knows of a fix, many thanks