Receiving 404 on certain installations from Trados Studio 2021 Translation Memory configuration form

One client is receiving a 404 error when configuring their KantanMT plugin.

Studio version: 16.1.3.4096

Plugin version: 4.1.0

The error only occurs on their installation and does not occur on any other device/installation even when tried with the clients credentials (API token).

Any suggestions much appreciated.

Colin