1) Put Upgrade folder in the ZIP Package
2) xoops_data and xoops_lib go in data.zip
3) In Upgrade.php we have written code for version 2.5.0 (for not to show the upgrade link)
4) We have added fix in Upgrade/upd-2.4.0-to-2.4.1 index.php. Replaced $checkbit with $func. check if upgrade works without this fix in next version
(4th step is not required from version 2.5.7. It works fine from 2.5.7)
5) XOOPS checks for illegal characters in path (which does not allow space) causing upgrade to fail hence we have added the same preg_match pattern in upgrade.php __requirements() function. Check if they update this pattern to allow spaces in future.
Taken from :
class/libraries/vendor/xoops/xmf/src/Xmf/Language.php
6) We do not configure include/license.php
7) PHP REQUIREMENT LINK : https://xoops.org/modules/core/