This thread is resolved. Here is a description of the problem and solution.
Problem:
The client was trying to activate the OTGS installer plugin to upgrade the WPML plugins.
Solution:
The OTGS installer plugin is only necessary when installing the WPML Multilingual CMS plugin. Once you've activated WPML Multilingual CMS, there's no need to activate the OTGS installer plugin since it provides the same functionality.
If you've registered WPML on your site, you can update it by going to the Plugins >> Add New page, clicking the Commercial tab, and then hitting the “Check for updates” button.
Relevant Documentation:
https://wpml.org/faq/install-wpml/#checking-for-updates
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