The only bug I see is that somehow their message wasn't displayed. If an AI declares war on you, you can't speak to it the same turn (or several turns after) without cheating/abusing exploits. Their communication to you in the case of a war declaration is very much just that: a declaration (very one-sided).
The other choice is "Done".
The AI will eventually grow bored of extorting you for money, and will then declare war on you without further notice (them extorting money was the notice). Also, an AI that has been paid by another race to declare war, can forego extorting money entirely. Sometimes they don't extort money to begin with, but decide that your planets (ALL your planets) are much better payment.
Annoying that you didn't get the text though...