Essentially, the number of units billed for the service code is incorrect. V23 is used for unit based codes when the number of units submitted is unusually high or low and has been flagged internally by the MOHLTC.
Double check if an entry error has been made. Resubmit with the correct units for the rejected code.
If the unit amount submitted is correct, fax supporting documentation and letter to your claim assessor and resubmit the claim with manual review.
Note, you may need to double check the Schedule of Benefits to confirm you are using the correct suffix (A instead of B or C for procedures that have two codes-one for the professional code and a separate code for the technical code).