Background of the issue:
I have cloned my site locally and created a development account to test my website in a staging environment. I am trying to upgrade my WPML plugins. The current plugin versions are: WooCommerce Multilingual & Multicurrency 5.3.6, WPML Media Translation 2.7.4, WPML Multilingual CMS 4.6.13, WPML SEO 2.1.1, WPML String Translation 3.2.14. My WordPress version is 6.8.1 and my PHP version is 8.3. The issue can be seen at enlace oculto.
Symptoms:
On attempting to upgrade, I received the error: 'Upgrade failed: Undefined'.
Questions:
Why did the upgrade fail with an 'Undefined' error?
How can I successfully upgrade my WPML plugins?