# wrapping long equation using square stretched bracket [duplicate]

How do we split long equation in which a command \left[ and \right] is used? My equation is as follow

\begin{align}
\begin{split}
z &=-2Re\left[B^\ast\left(\frac{1}{2}\sum_{k=0}^{N}\alpha_k\zeta^{1-k}\left(1-is_1\right)+\alpha_k\frac{1}{\zeta^{1-k}}\left(1+is_1\right)+\beta_k\zeta^{1-k}\left(i+s_1\right)+\beta_k\frac{1}{\zeta^{1-k}}\left(s_1-i\right)\right)\\
&+\left(B^{\prime\ast}+iC^{\prime\ast}\right)\left(\frac{1}{2}\sum_{k=0}^{N}\alpha_k\zeta^{1-k}\left(1-is_2\right)+\alpha_k\frac{1}{\zeta^{1-k}}\left(1+is_2\right)+\beta_k\zeta^{1-k}\left(i+s_2\right)+\beta_k\frac{1}{\zeta^{1-k}}\left(s_2-i\right)\right)\right]
\end{split}
\end{align}

LaTeX complains because the \left[ and \right] command are now separated by the \\. I am also using split command, unlike other identical post.

I am using \usepackage{amsmath}

I use \left[ and \right] because I must stretch the bracket; unless there is another way to do it. Could anyone help me, please?