The most common — and least informative — decline on earth. The issuer is saying "no, and I won't tell you why." Usually the issuer's fraud model didn't like something: the merchant, the amount, the time, the location. Deliberately vague so fraudsters can't learn the rules.
The classic soft decline. Wait and retry once (many recover within 24–72h), or ask the customer to try another card or contact their bank. If your business sees spikes of 05s, your MCC or descriptor may be tripping issuer risk models.
A soft decline: the condition is temporary. A retry — later, or with a different method — can legitimately succeed.