This thread is resolved. Here is a description of the problem and solution.
Problem:
You are trying to update the WPML plugin but encounter an error stating 'Unable to register: Site key not matching' even though you are entering the correct product key.
Solution:
1. Navigate to Plugins → Add New and select the Commercial tab. Then, click 'Unregister WPML from this site'.
2. After the page loads, click on 'Register WPML'. You will see a prompt to enter the site key. Select 'Get a key for this site'.
3. In your WPML account, complete the site key wizard and set it to 'Production site'.
4. Copy your new key and paste it in the Commercial tab. Afterwards, you can delete your old site key in the WPML account.
If this solution does not resolve your issue or seems outdated, we recommend checking related known issues at https://wpml.org/known-issues/, verifying the version of the permanent fix, and confirming that you have installed the latest versions of themes and plugins. If the problem persists, please open a new support ticket.
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