In standard Claim management configuration in Project systems 4 details text area in addition to "Long Text for Header" which is the default text element. The remaining 4 text elements can be configured based on user requirements.
Note : Only a maximum of 4 text area can be configured as per standard.
Detailed text in claim management is linked to catalog and catalog groups which is different from other long text configuration.
Additional long text for claim is derived from configuration table assigns Catalog + Code Grp + Code for each additional long text. A maximum on only 4 long texts can be maintained.
You can define a code group in any of the standard catalog and link in in this configuration table. But for best practice purpose , create a new catalog Type called " Additional Text" and create specific code groups / codes and link to this table. In standard Catalog type 'C" has a code group CLM-01 for additional text which can also be used.
In case you want to modify or add additional long text , navigate to maintain Catalog --> Edit Catalog and select catalog "C"
Navigate to Coded menu and add additional text required