Envelope-level error → taxonomy. PayZen prefixes announce the origin: INT_ (merchant integration), PSP_ (gateway), ACQ_ (acquirer decline), AUTH_ (3DS), CLIENT_ (browser). New codes appear over time — unmapped PSP-side codes degrade to a non-retryable processing_error.
Envelope-level error → taxonomy. PayZen prefixes announce the origin: INT_ (merchant integration), PSP_ (gateway), ACQ_ (acquirer decline), AUTH_ (3DS), CLIENT_ (browser). New codes appear over time — unmapped PSP-side codes degrade to a non-retryable processing_error.