Instruction Fallback (Anchor)
Programming Model · Abyss
Anchor's default error handler that triggers when incoming instruction data doesn't match any registered 8-byte discriminator. Returns error code 0x65 (101) with message 'InstructionFallbackNotFound'. Most commonly seen when a client sends a discriminator format the program doesn't understand — e.g., a V2 single-byte disc to an Anchor V1 program expecting 8-byte SHA256 discriminators. Native Solana programs handle unknown discriminators with their own match logic.