Two PDT failures in August, one PDT and one IPN Invalid on the same day (different orders) in September; otherwise all notifications succeed. I notice that the Paypal 'recieve messages setting is disabled. I'm not sure what that function does, but I have now set it to active.
looking at the paypal notification hsitory I see that the two below are marked as 'Recurring payment agreement expired';presumanly this is the message that was not sent because I had the function disabled;
However, I have just 'resent' the notification that failed on 10/10/2023 which provoked this post and it arrived 'verified' (though CBSubs says 'IPN Basket non-existant'. ILooking closer, I see that this too was a recurring payment transaction. It now seems that all these failed notifications are the result of subscribers having two spearate payment profiles. one of which is going to the old website; so this problem is the result of moving a website; previously existing PayPal recurring payment profiles no longer function ... I thought I'd resolved all such accounts, but clearly there are still some lurking;
I'll mark this post as 'solved'