How sound are the phrases mentioned in the supplication of Hizb al-Nasr attributed to Abu al-Hasan al-Shadhili?

This supplication is one of the innovated supplications and has no basis in the Sunnah (definition). Designating it for a specific purpose, adhering to it, and believing it to be Sunnah, renders it an innovation (bid'ah). It contains other prohibitions, including supplicating with verses whose knowledge God has exclusively kept for Himself, such as the disconnected letters at the beginnings of surahs, supplicating with the third-person pronoun (He), and seeking intercession through the "secrets" of these supplications. The permissible form of intercession is only seeking intercession with God through His names and attributes, and seeking intercession with Him through righteous deeds.