Only uppercase characters possible in 3-character units of measurement

What causes this issue?

You wanted to represent a commercial (3-char.) measurement unit format
with the text &V1&. This text contains lower-case letters.
Only upper-case letters are allowed in the commercial (3-char.)
measurement units. Lower-case letters are only allowed in the technical
(6-char.) format.

System Response

The representation can not be saved like this, otherwise the data
would be inconsistent.

How to fix this error?

Please check the representation, and change the 3-character
representation for the following entry:
&V3&

Error message extract from SAP system. Copyright SAP SE.