Field name not allowed

What causes this issue?

You have specified a field name, the syntax of which is not correct.
Fields are placeholders in texts, the value of which cannot be
determined until the form is processed. Field notation is carried out
using <ZH><(>&<)>Field name&.</>.

System Response

The operation was rejected.

How to fix this error?

Enter the correct syntax for a field in the notation <ZH>
<(>&<)>Field name& </>.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.