solved my problem with another function :
https://mymoodle.com/webservice/rest/server.php?moodlewsrestformat=json&wstoken=mytoken&wsfunction=core_user_get_users_by_field&field=email&values[0]=myemail
core_user_view_user_profile -> core_user_get_users_by_field
https://mymoodle.com/webservice/rest/server.php?moodlewsrestformat=json&wstoken=mytoken&wsfunction=core_user_get_users_by_field&field=email&values[0]=myemail
core_user_view_user_profile -> core_user_get_users_by_field