PHP@7.1 is deprecated https://www.php.net/supported-versions.php.
So try to install with other repo
1 brew install openldap libiconv 2 brew tap exolnet/homebrew-deprecated 3 brew install PHP@7.1
https://devhoi.com/threads/install-brew-deprecated-php-version-php-7-1-5-6-7-0-on-brew-macos.25/