We will be handling your issue via your Ticket instead of here to avoid duplicate responses.

We could not find anything in regards to this issue. The IPNs which we needed to review had long since been purged by PayPal (they only keep 1 months worth of IPNs). We suspect some sort of configuration issue (e.g. changing a price after someone has subscribed or changing price at PayPals end).

the problem was, that in the beginning I only had a net price (24,- €). After a few month the advanced tax function in CB subs was included. Then I added the tax to the price (the plan price keep always the same). So old subscriber paid 24 € and new one 24+taxes.

This causes a price mismatch and will invalidate the IPN. For example PayPal sends CBSubs $30 or $5, but the plan is $25. CBSubs has no choice but to invalidate it, because it didn't match. If you need to change the price you should discontinue the plan in favor of a new plan or cancel everyones recurring profiles so they can renew at the new price.

PayPal does not allow recurring profile changes beyond 30 days. So after those 30 days it's impossible to change a price on PayPals end. It has to be cancelled entirely. I think we need to implement more warnings when pricing adjustments are made with active subscriptions (this includes CBSusb Tax and CBSubs Promotions adjustments).

The next issue was that the subscription end mails often send completly confusing. Often a view monthes after subscription ends.

This is due to not triggering expirations. You need to visit CBSubs backend regularly, setup frontend to trigger expirations, or run the expiration processing URL through CRON regularly. This is all explained in your documentation. If you have any grace periods then that'll also effect expirations as they don't actually expire until the grace period is up.

Here I got no answer from CB team.

Because you opened a private ticket in addition to this topic. We replied to you in the ticket.