POS Terminal Error Codes: Payment Processing, Connectivity, and Device Health

Use this guide to separate issuer declines from terminal connectivity and device health states so you can restore acceptance safely.

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TL;DR

✓ Separate: card decline vs host connectivity vs device health (tamper/keys).
✓ If many cards fail at once, suspect connectivity or host outage.
✓ If one card fails everywhere, suspect issuer/account state.
✓ Do not DIY security/key handling; follow vendor/processor procedures.

Quick Navigation

Symptoms Root Causes Step-by-step fixes What NOT to do If it persists Code directory Related guides & hubs FAQ References

Symptoms / When you see this

✓ Host unavailable/timeout/communication errors.
✓ Tamper or keys-not-loaded messages.
✓ Repeated declines with issuer codes.
✓ Settlement/batch close failures.

Root causes (grouped)

✓ Issuer declines and risk decisions.
✓ Host/gateway connectivity failures.
✓ Key state and terminal security health (tamper, keys).
✓ Duplicate/reversal state after interrupted transactions.

Step-by-step fixes (safe, prioritized)

✓ Verify internet and host connectivity if many transactions fail.
✓ Restart terminal and network equipment.
✓ For tamper/keys issues, remove terminal from service and contact vendor/processor.
✓ For declines, confirm entry method and ask customer to contact issuer if persistent.
✓ Follow reversal prompts and verify transaction final state before retrying.

What NOT to do

✓ Do not open terminals or attempt key repairs.
✓ Do not repeatedly retry after timeouts without verifying previous state.
✓ Do not store sensitive payment data outside approved systems.

If it persists (escalation checklist)

✓ Capture message/code, timestamp, amount, entry method, terminal ID.
✓ Check if other stores are impacted (outage).
✓ Use processor support for key reload and settlement issues.

Code directory within this guide

✓ Some systems have both “POS terminal” and “POS response” codes. Use code page context to confirm layer.

Code	Meaning	Next step
ICC READ	Chip read error — The terminal could not read the EMV chip data from the card.	Follow the checklist on the code page
DUPLICATE	Duplicate transaction — The terminal/processor detected a potential duplicate transaction and blocked it to prevent double-charging.	Follow the checklist on the code page
EMV FALLBACK	Chip fallback — The terminal could not complete a chip read and is requesting a fallback method per EMV rules.	Follow the checklist on the code page
MAC ERROR	Message authentication error — The terminal or host detected a message authentication (MAC) validation failure.	Follow the checklist on the code page
NO CONNECTION	Host connection unavailable — The terminal cannot reach the payment host/gateway to authorize the transaction.	Follow the checklist on the code page
PIN PAD	PIN pad inoperative — The PIN entry device is not available or not responding, so PIN-based transactions cannot proceed.	Follow the checklist on the code page
REVERSAL	Reversal required — The processor indicates a reversal/void is required to correct an incomplete or errored transaction state.	Follow the checklist on the code page
SIGNATURE	Signature required — The transaction is approved or conditionally approved but requires signature verification per the processing rules.	Follow the checklist on the code page
SWIPE READ	Magstripe read error — The terminal could not read the magstripe data from the card during a swipe.	Follow the checklist on the code page
TAMPER	Tamper detected — The terminal detected a tamper condition and disabled sensitive functions to protect encryption keys.	Follow the checklist on the code page
BATCH NOT CLOSED	Settlement pending — The terminal indicates settlement/batch close was not completed successfully.	Follow the checklist on the code page
CALL ISSUER	Issuer contact required — The terminal indicates the issuer requires the cardholder to contact them before approval.	Try another method; contact issuer if it follows the card
COMMUNICATION ERROR	Host communication failed — The terminal could not communicate with the processing host to complete the request.	Follow the checklist on the code page
DECLINED	Issuer declined — The terminal indicates the payment was not approved by the issuer.	Try another method; contact issuer if it follows the card
HOST UNAVAILABLE	Host unreachable — The processing host was not reachable during the transaction attempt.	Follow the checklist on the code page
INVALID TID	Terminal ID invalid — The terminal configuration did not validate the terminal identifier for processing.	Follow the checklist on the code page
KEYS NOT LOADED	Encryption keys missing — The terminal is not ready to process because required keys are missing or not current.	Verify the correct path/resource and prerequisites
PAPER OUT	Receipt paper empty — The terminal or attached printer cannot print receipts because paper is missing.	Verify the correct path/resource and prerequisites
TIMEOUT	Request timed out — The terminal did not receive a response within the allowed time window.	Retry once; validate connectivity and service status
UPDATE REQUIRED	Update needed — The terminal indicates a required software or configuration update must be applied first.	Confirm storage/prerequisites; retry after restart
00	Approved — The authorization was approved and the transaction can proceed.	Follow the checklist on the code page
01	Refer to issuer — The transaction requires additional handling; the merchant may be instructed to contact the issuer.	Try another method; contact issuer if it follows the card
03	Invalid merchant — The merchant identifier or acquiring setup is not recognized or not permitted for this transaction.	Follow the checklist on the code page
04	Pick up card — The issuer indicates the card should be retained and the transaction should not proceed.	Try another method; contact issuer if it follows the card
06	Error — A generic issuer or network error occurred; the transaction could not be processed as submitted.	Try another method; contact issuer if it follows the card
07	Pick up card (special condition) — The issuer indicates a retain/pick-up action under special conditions; the transaction should not proceed.	Try another method; contact issuer if it follows the card
15	No such issuer — The card issuer could not be identified or the routing information was not recognized.	Try another method; contact issuer if it follows the card
30	Format error — The authorization request format was invalid or could not be parsed by the receiver.	Follow the checklist on the code page
41	Lost card — The issuer indicates the card is reported lost; the authorization should be declined.	Try another method; contact issuer if it follows the card
43	Stolen card — The issuer indicates the card is reported stolen; the authorization should be declined.	Try another method; contact issuer if it follows the card
05	Do not honor — A card transaction was declined with a non-specific “do not honor” response.	Try another method; contact issuer if it follows the card
12	Invalid transaction — The transaction type or requested operation was not accepted for processing.	Follow the checklist on the code page

Tip: If your exact code isn’t listed, use the closest hub link above and browse related prefixes or message patterns.

FAQ

Is “declined” always terminal fault?

No. Declines are commonly issuer decisions. Terminal faults are more likely when many cards fail or connectivity messages appear.

What does “tamper detected” mean?

A security mechanism triggered and disabled sensitive functions. It often requires certified service or replacement.

Can I fix keys-not-loaded myself?

Usually no. Key handling is compliance-sensitive; follow processor/vendor procedures.

Why do timeouts cause duplicates?

If host response is interrupted, the terminal may not know the outcome. Reversal/duplicate prevention prevents double-charging.

Safest retry rule?

Retry once after confirming connectivity. If outcome is unknown, verify state before retrying.

Why does chip fail but tap works?

Chip contact issues or reader wear can cause read failures; contactless may still work depending on rules.

When should I call processor?

For outages, key issues, settlement failures, and widespread declines with network errors.

What should I log?

Terminal ID, timestamps, response text, and whether failures are widespread.

References / Notes

✓ Processor support guidance
✓ Terminal vendor documentation
✓ PCI and key-handling policies