I have noticed when I go past my daily Curve limit, the payment page in a browser still takes me through 3DS (which I generally use as ‘push’ approval to the Curve app). The merchant then advises its been declined.
The transaction information in the Curve app should tell you more about why it was declined. For example, regarding limits, any other Curve things and then also information (where received from the underlying card issuer) if Curve isn’t responsible for the decline.
In essence, even if it just started with “you’ve hit limits!” that would same some effort.