Output length (&) is less than the calculated output length (&)

What causes this issue?

The output length is calculated from the specified data type, number of
positions, decimal places and sign.
The output length specified is below this calculated output length.
This means that only the part of a value is displayed which is in the
area of the specified output length.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Increase the output length.

Error message extract from SAP system. Copyright SAP SE.