"free" as in a free 2-year subscription that came with the £50 printer (HP Envy 5050, from memory it was reduced to about £30). I've been paying nothing. I'm noticing that they're much less generous than they used to be with that offer, and 9 months is now more likely.
They also changed Instant Ink midway through and offered cheaper tariffs for fewer printed pages. So technically I had a £x credit that I've eked out to be about 2.5 years. They'll ask me for payment details next month to carry on using it, and I've had this printer since before the pandemic. I think I've done all right for £30.