The honest decline: the money isn't there right now. The single biggest cause of failed subscription payments — and the most recoverable.
The dunning workhorse: retry on a smart schedule (paydays — the 1st and 15th — outperform), or offer to split the amount. Recovery rates of 30–50% on 51s are normal with good retry logic.
A soft decline: the condition is temporary. A retry — later, or with a different method — can legitimately succeed.