People's pension error message:
H/C03 - File start date is different to your account settings - Provided value 'YYYY-MM-DD' - Expected value 'YYYY-MM-DD'
H/D03 - File end date is different to your account settings - Provided value 'YYYY-MM-DD' - Expected value 'YYYY-MM-DD'
The issue is caused by the period dates you are submitting, which do not match those the People's Pension is expecting. This could be a full period out if you are submitting having missed the last period, or a duplicate submission of the previously accepted period.
You may also get these messages if you try to submit two periods on the same day. People's can only accept one submission per day per scheme as they complete the processing overnight.
If you need to, you can contact People's Pension support to change the period dates on the scheme records, or adjust in payroll if required.