Value "&" is incompatible with template "&"

What causes this issue?

The value you entered does not correspond to the template defined
for the characteristic format.

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?

Correct the value according to the template shown in the error message.
For further information, press F1 to refer to the online help.

Error message extract from SAP system. Copyright SAP SE.