Dear Lara,
Thank you for your email.
We are presently working on the upcoming Newspapers Thematic Collection which is soon planned to be release. Once released, you will be able to filter on Newspapers like you can do for other Thematic Collections.
In the meantime, you can query/filter on the datasets that are expected to be part of the Collection, like you did. In specific about your query, you are missing a wildcard at the end since the name of the dataset does not end with "Newspapers", it should therefore be as follows (I faceted on the field just to show you the full name of the dataset):
I would like to ask to not "widely" share your API key as we use them to get quality of service statistics.
If you have any questions, please let us know!
Sincerely,
The API team