Simultaneous proceedings

(a) Except as otherwise provided in § 26-5B-204 , a court of this state may not exercise its jurisdiction under this article if, at the time of the commencement of the proceeding, a proceeding concerning the custody of the child has been commenced in a court of another state having jurisdiction substantially in conformity with this chapter, unless the proceeding has been terminated or is stayed by the court of the other state because a court of this state is a more convenient forum under §