SSH access on VMG8623-T50B

Hello all,
I've enabled ssh access on my router the zyxel VMG8623-T50B through the web interface.
But when I try to login, the password is not accepted.
Is there a prefix I should add to my passsword ?
for example if my password is "1234" then the ssh password is "soho1234" ?

I would appreciate any help. 
Thank you