Error in an arithmetic operation or a data conversion

What causes this issue?

The self-defined conversion routine for the field &V1& tried to execute
an invalid arithmetic operation or an invalid conversion of data types.

System Response

The IDoc processing was terminated and defined as incorrect. You can
always reimport the IDoc at any time.

How to fix this error?

Check the accuracy of the self-defined conversion routine for the field
&V1&. Make sure that the used data types and lengths match the
definition of the InfoSource.
Correct any data errors and restart processing for this IDoc.
If the problem continues to occur, search in the SAP Support Portal for
the relevant notes and create a customer message if necessary.

Error message extract from SAP system. Copyright SAP SE.