This purchase is not supported You already own InDesign.

If you have an active subscription already, go to your account.adobe.com and check what you status is and what you may have purchased already. ("Plans and payment" and "Products"). All the info you require should be there.

Just in case it's not clear: you don't "buy" any particular version of InDesign, or any other Adobe tool these days. You pay for a subscription, and as long as the subscription is valid (paid up), you can download and use any current version of any tool it covers. (And, sometimes, older versions, when you need backwards compatibility).

The whole CC subscription covers something like three dozen apps (ID, Illustrator, Photoshop and all the video tools, to start with); there is also an InDesign subscription that includes ID, InCopy, Acrobat Pro and I'm not sure what else.

So if you have a subscription... go to your system copy of Creative Cloud, and you can manage your current apps from there.

On which OS an version of the OS? Mac, Windows? Some computers/OS are no longer supported in 2023, so that also could be the case... 

When you say you want to upgrade to InDesign 2023, does that mean you already have an earlier version of InDesign CC? Is it an InDesign only subscription, or through a Creative Cloud account?

Unusual... do you already have a paid subscription (either to Creative Cloud All Apps or InDesign)?

If so, you should not take out a second subscription, you will pay twice forever.

Just upgrade. If you get an error when upgrading, please let us know the details.