I think the line item is present in the INV02 Country Summary as Safety Stock flag count - Formula 'INV01 Inventory Ordering'.Safety Stock exception count[SUM: 'SYS08 SKU Details'.Country Made In].
The formula is exact. Check with the format. Also if you can attaché the error that you are encountering that would help us to find the exact issue. Also please check the line items names that should match in the formula(Capital letters, small letters or spelling check)
Without seeing the error message it is challenging to give you an exact answer.
However, check through the following;
Is the dimensions of the mapping module the same as the source module, INV01? From your query this should be the list, SKU Details.
is the dimension of the target module the same as the line item in your mapping? From your query this appears to be, Country.
The above checks form the key bridge in connecting the source dimensions with those in the target. Without them the SUM functions will simply not work. If this is the case you should receive a mismatch of dimensions error.
Are you clicking through each element of the formula rather than writing in out? Differences in spelling and the absence of apostrophes ( ' ) for non numerical characters can cause errors. From your query I do not believe this is the issue.