Hi,
as I read in SAP note 1779311, 'The highest amount the system can handle is 99.999.999.999,99 (11 digits + 2 decimals). It is not possible to extend the WRBTR/DMBTR fields lenght: the amount that you can insert into a document cannot be longer than 13 digits. These fields remain defined as CURR 13 digits in the BSEG (the most important table for the postings).'
there is also the solution proposed in this note how to overcome the issue if required.
Kind regards,
Renatas