I have following text in a parameter "Notification 3013495 saved"
When I write it out with "Message" I only get "Notification".
What have I done wrong?

Probably the inverted commas / quotation marks "..." are missing around the variable.

If a variable V[msg] has the value "Notification 2013495 saved",

Message "&V[msg]"

will output the whole string, but

Message &V[msg]

will be interpreted as

Message Notification 2013495 saved

which for GuiXT is equivalent to

Message "Notification" "2013495" "saved"

and will output "Notification" only.