Let's follow up this discussion at the Neptune Community
(this forum will be kept in read-only mode)
in the SAVE_TEXT method of the class ZCL_NAD_CS_NOTIFICATION the CONVERSION_EXIT_THHMM_OUTPUT is recalled but it doesn't exists in the system.
Changed to CONVERSION_EXIT_HH_MM_OUTPUT.
(notified by a customer).
Thank you very much Andrea.
The app has been changed and re-published in Neptune App Store.