POS Terminals Error Code
Systems & Devices
POS Terminals
MAC ERROR | Message authentication error
Industry
Systems & Devices
Canonical
/systems/pos-terminals/error-codes/mac-error/
Last Updated
Feb 27, 2026
Summary
The terminal or host detected a message authentication (MAC) validation failure.
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What This Code Means
MAC errors in payment environments indicate that a cryptographic message authentication check failed. This can occur when terminal keys are not synchronized with the host, when a message was corrupted in transit, or when security configuration is inconsistent.
Where Users Usually See This Code
- During secure transactions requiring MAC validation
- After key injection or key rotation events
Why This Code Appears
- Terminal keys are missing, expired, or incorrect
- Host and terminal key sets are out of sync
- Communication corruption or protocol mismatch
What Typically Happens Next
- Transaction fails and terminal may require key reload
What This Code Is Not
- It is not a customer card decline reason
- It is not safe to attempt security repairs without vendor guidance
Troubleshooting Checklist
- □ Confirm terminal keys are loaded and current
- □ Contact processor/vendor for key reload procedures
Notes And Edge Cases
Key handling is compliance-sensitive; follow certified procedures provided by your processor/vendor.
Related Codes
8 links
- COMMUNICATION ERROR CodeHost communication failed
- DECLINED CodeIssuer declined
- KEYS NOT LOADED CodeEncryption keys missing
- BATCH NOT CLOSED CodeSettlement pending
- HOST UNAVAILABLE CodeHost unreachable
- ICC READ CodeChip read error
- NO CONNECTION CodeHost connection unavailable
- SWIPE READ CodeMagstripe read error
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