What's wrong with my user registration & confirmation

hi all

i need to understand the user CONFIRMATION

I use open registation with email

so to do a user creation :

i do a POST to /api/v2/user/register
with

'email': email,
"first_name": fistname,
"last_name": nom,

the user receive en Email with confirmation code no problem here.

and now i want to confirm without the dsp confirmation page
so i build a page who do a post to /api/v2/user/register
with

'email': email,
"code":code,
"new_password":password

and i got an error that tell me that the email is already taken (like if i'm doing a create user)
is there any other way to do user confirmation?

thanks