Field &1: External length &2 greater than &3 for appl. data element &4

What causes this issue?

The format of field '&v1&' may be incorrect. For external
representation of a field, an ABAP data type is converted into a text
field. The external text field must have a minimum length so that a
loss-free transfer is possible between the two fields.
The data element '&v4&' stated requires '&v3&' character places
externally. However, only '&v2&' character places are defined in the
repository structure.

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

System Response

How to fix this error?

Please check whether there was a change in a domain or a data element
and whether the difference determined was caused by this.
Change the data element used or use another data element, as necessary.
If processing or application logic demonstrates that no format
violations arise, no change is required.
If external standards must be adhered to, it may be necessary to define
the external field longer than the internal. Ensure, however, that an
appropriate format conversion takes place in processing.

Error message extract from SAP system. Copyright SAP SE.