404 on preview if k2 item not published

You do not have an active subscription for Better Preview.
There is no support for K2 in the free version of Better Preview and only partial support in the Pro version.

Like mentioned in the previous message, there is only partial support for K2.
The way K2 works, makes it impossible (read: really hard and not worth the effort) to make things work 100%.
Also K2 has changed its way of doing things numerous times, making it necessary to hack around those changes again and again.

If you want, I can give you a refund again, like last time when you figured out Better Preview was not what you wanted in combination with K2.

I will remove all mentions of K2 in the Better Preview descriptions and docs to not give the expectation that it fully works.

Done.