You can't condition service on consent (if you only need the consent for revenue, not in order to provide actual service)

What is "the service"? Why can't personalized ads be part of my service? I can how selling personal data isn't part to the service, but the ad content displayed to a user is.

If you're a newspaper for example, personalized ads isn't part of your service which is to present news. So you can't make presenting the news conditional on accepting ad tracking.

You're free to have ad tracking as long as it is optional and by explicit consent only.

But you can use a paywall... So can you say 'pay, with either cash or personal information'?

I just said GDPR legislates that personal information is not a form of currency, so no, you can't ask for payment in the form of personal information.

Really? So you can no longer have opt-in ads, or a 'premium' ad-less version?