Custom packages from AUR is unstupported so if you cannot make the script work - get in touch with AUR maintainer.
You should learn how build packages by reading the articles on Arch Wiki.
https://wiki.archlinux.org/title/Arch_User_Repository
PHP56 is long deprecated - the version in the repo is v8.
https://aur.archlinux.org/packages/php56
git clone https:://aur.archlinux.org/php56.git
cd php56
makepkg -is