Issuing a Warning Letter for Process Violation
Yours appears to be a company from the hospitality industry. If you want a warning letter to be issued for the violation of the laid process, first enumerate what the process is. Then, write the specific instance, i.e., date and time of the default, and how the procedure was violated. Later, give the warning.
Nevertheless, this appears to be a serious matter. Serving food to the guests without uploading the software is bypassing the system. How was the lapse discovered? The value of the transaction could be small, but the lapse casts light on the integrity of the person. Issuing a warning letter is as good as condoning the lapse that could have deprived revenue from your organization. Therefore, you may review your decision to issue a warning letter.