Two different questions
Authentication asks whether there is sufficient confidence in the person or credential behind a purchase. Authorisation asks whether the issuer approves this particular payment. A checkout can pass the first stage and fail the second without either system being broken.
Where 3DS fits
EMV 3-D Secure exchanges information to support authentication for online card payments. Some journeys involve an additional customer challenge; others do not. Record the authentication result separately from the later payment response, with timestamps and a shared purchase identifier for investigation.
A checkout example
Imagine a customer completing a banking-app challenge for a €120 purchase. The subsequent authorisation is declined. The support team should inspect the payment response and available processor detail before requesting another challenge. Repeating authentication alone does not resolve every issuer decision.
What to measure
Build separate funnels for authentication completion and authorisation approval. A drop between those stages suggests different questions from a drop inside the challenge journey. Compare like payment populations, and keep technical errors separate from explicit decisions so that ownership of the problem remains clear.