Error:
CMN.ATO.CTR.500231 - Tax loss 2019-20 carried back to 2018-19 must be provided.
Solution:
Leave items A and O blank and validate. Refer to below snip.
Note that you need to put the Aggregated turnover range in the "Financials" tab.
A validation message can be clicked and it will point to empty field. Also a note is added which describes the situation.
Related guides:
Loss carry-back offset (eligibility requirements)