After e-junkie payment, send a http post to register user automatically?

How about using wp_create_user() and then add_user_meta()? Between those two, you should be able to store all the data you get back, and even store it in fields wordpress uses natively.

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)