Missing quote mark

What causes this issue?

The syntax check noticed that inverted commas were missing.

System Response

The cursor shows the inverted comma which does not have a closing
inverted comma.

How to fix this error?

Check your entries and enter the missing inverted comma if appropriate.
Please note that a symbolic characteristic value should always be
entered as a character string in inverted commas.

Error message extract from SAP system. Copyright SAP SE.