I uploaded the module but PrestaShop says "unable to install module."

Module installation usually fails because PrestaShop cannot read the archive, cannot write the module files, or the module cannot run on the current server.

Check the ZIP structure first. The archive should contain one module folder at the top level, with the module's main PHP file inside it, for example mymodule/mymodule.php. A common failure is uploading a GitHub-style ZIP that contains an extra wrapper folder, documentation folder, or a nested module folder instead of the actual installable module directory.

zip=module.zip
unzip -Z1 "$zip" | sed -n '1,20p'
unzip -Z1 "$zip" | awk -F/ 'NF{print $1}' | sort -u
find modules -maxdepth 0 -writable -print
php -v
php -m | grep -Ei '^(zip|curl|dom|fileinfo|json|mbstring|openssl|intl)$'
ls -lt var/logs/* 2>/dev/null | head

• Check upload limits: the effective limit is controlled by upload_max_filesize and post_max_size. If the ZIP is larger than either value, the back office upload can fail before PrestaShop even installs the module.
• Check permissions: the modules/ directory must be writable by the web server user, and cache/log directories must also be writable.
• Check PHP compatibility: wrong PHP version or missing PHP extensions such as zip, curl, dom, fileinfo, json, mbstring, openssl or intl can break install or configuration screens.
• Check PrestaShop logs: look in var/logs/, the back-office error page, and the web server/PHP-FPM error log for the real exception.
• Clear cache after fixing a failed install, because PrestaShop may have cached a partially loaded module class.

If the module appears in the module list but will not install, the archive was probably extracted successfully and the failure is inside the module install routine. If it never appears at all, focus first on ZIP structure, upload limits and filesystem permissions.

If the install routine fails after the folder was already extracted, first remove the half-installed module from Module Manager if it is visible, then clear var/cache/ before trying again. If the module row exists in the database but the back office cannot load the module page, do not keep retrying blindly; restore the file/database backup or ask support to check the failed install() step.

When contacting support, send the module ZIP name and version, your PrestaShop version, PHP version, the exact error text, the last lines from var/logs/prod.log or var/logs/dev.log, and whether the module folder now exists under modules/. That tells support whether the failure happened during upload/extraction or inside the module's own installer.