Sorry, posted by mistake and then timed out for editing!

Have a Toshiba CIX100 + LUCA Strata messaging voicemail
Extension 724 has did
Extension 725 no did
Hunt group 510, 724 and 725 as members
When a call comes in both sets ring, perfect
Trying to put 724 message waiting indicator on 725 in EManager but get an error, The Prime DN entered conflicts with a value of an existing numbering scheme.
What is the correct way to get a message waiting light for another extension on an extension with no voice mailbox?

Thanks

George