Make sure it says from January to December, as shown below:
Fiscal Date, From: 01/01/2021
Fiscal Date, To: 31/12/2021

If the dates were entered in the wrong order, this would cause the software to reject the fiscal period, as it would be incorrect.

Since a fiscal period is usually 12 months, if your fiscal period end date was December 31st, then the start date should be January 1st.

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