Use the fully qualified table name in the table property, e.g:
ATTACH INPUT ADAPTER MyInput TYPE db_in
TO MACHINE_REF_window1
PROPERTIES
table = 'MY_STREAMING_USER.MACHINE_REF' ,
service = 'hanaservice' ;
In the example above, the table MACHINE_REF is in the HANA database schema called MY_STREAMING_USER
You raise a good point though: this is not obvious and is not documented. I'll get it added to the documentation.
Now if this doesn't fix the problem, it could be a problem with the field mapping. If so, and if you are using HANA studio with the streaming plugin, an easy thing to do is let the Studio create the input stream/window for you, defining the schema to match the HANA table: just open the streaming project in the visual editor, then go to the HANA Systems view, find the table you want to use for input, and drag it into the streaming project diagram. If you are using ESP Studio, then sorry, this trick isn't available and you'll just have to troubleshoot your field mapping.
P.S. - I noticed that you posted this in the "Event Stream Processor" space. This space is really intended to share non-technical information and isn't monitoring by the tech-team. In the future, please post technical discussion items to the Streaming Developer Center: Smart Data Streaming Developer Center