Cost of sales must always be settled completely

What causes this issue?

You want to settle the cost of sales for a sender. Note that the costs
must always be settled 100%.
In the settlement rule for the sender one of the following situations
exist:
The sum of the percentage rules is not 100%
Only one amount rule exists

How to fix this error?

Change the distribution rule of the sender so that
At least one rule exists with an equivalence number or
The sum of the percentage rules amounts to 100
If you are using a source structure, each source allocation must be
settled completely.

Error message extract from SAP system. Copyright SAP SE.