PayPal-Request-Id caps at 38 single-byte characters. Short keys pass
through untouched; longer ones collapse to a SHA-256 prefix — the same
PayFanout idempotencyKey must always yield the same header value, so the
derivation is deterministic, never random.
PayPal-Request-Id caps at 38 single-byte characters. Short keys pass through untouched; longer ones collapse to a SHA-256 prefix — the same PayFanout idempotencyKey must always yield the same header value, so the derivation is deterministic, never random.