Error report · Service, fee & diagnosis
OHIP error code AT1
Only One Modality Allowed
What AT1 means
The Ministry of Health’s official wording for AT1 is: “Only One Modality Allowed.”
This code appears on your Claims Error Report (downloaded through MCEDT). It means the claim was rejected at submission and was never adjudicated for payment — fix the issue below and resubmit the claim.
How to fix AT1
Only one modality is allowed - submit a single modality for the encounter and resubmit.
These codes relate to the fee schedule code, diagnosis code, fee amount, or service limits in the Schedule of Benefits. The fix usually starts with re-reading the code's payment rules — effective dates, age/sex limits, maximums, and combinations — for the date of service.
Related codes
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Code meaning per Ontario Ministry of Health — Error Report Rejection Conditions / Error Codes (December 2022). The suggested action is general information for Ontario physicians, not billing, legal, or tax advice — codes and rules change, so verify against the current Ministry of Health documents before relying on a claim.