The message has embedded spaces. This is not legal in a URL.

Message = "Dear  " & rowname & ",  your appointment has  been register at : " & rowtimerdv & " Contact us for any changes. Merci"
Spaces must be converted to %20 in a URL. Do this after the URL is complete:

            URL = Replace(URL, " ", "%20")
I am still getting automation error with your code, still trying to figure out what else is wrong.