Thank you Tobias.
I did that and thy came back to me with the following answer:
If you are using server side processing see this FAQ:
Q. How can I export the whole table when using serverSide and Buttons.
A. Buttons is a client-side process, so it can only export the data available at the client-side. When server-side processing is enabled, the full data set is not held on the client-side, so only the visible data can be exported. You can either: 1. Use a server-side process to create the files to download (recommended) or 2. Disable server-side processing.
Over to you ??
