Error codes / Anchor framework
InstructionFallbackNotFound
Anchor framework · Custom(101) · 0x65
custom program error: 0x65
What it means
Fallback handler not found for unrecognized instruction.
What to do
The instruction discriminator does not match any handler — check IDL or client version drift.
Have the transaction that failed with this?
Paste its signature. TxWhy shows the exact instruction and inner call that raised the error, and rebuilds the transaction when the cause is one it can fix (compute limit, expired blockhash, priority fee, stale swap quote).
Code 101 means something else in other programs
Custom codes are private to each program. Check which program actually raised it: it is the innermost failed call, not necessarily the program you called.