Two things.
First, just to clarify, if you’re using any character that confuses the WordPress parser, such as arrow brackets (< or >, for instance) you need to URL-escape those characters in the shortcode so that WordPress will pass the full shortcode and its attribute and values correctly to the plugin to handle. See the very last FAQ entry, headlined “Why am I getting errors when I try to use the query attribute?”
Second, it seems to me like you’re going about this in a way more complicated fashion than necessary. If I understand your question on Stack Exchange question correctly, all you need to do is retrieve a subset of data, but you’re trying to generate that subset as part of a query in the retrieval URL. You can do this, but as you’re finding out, it’s unnecessarily complicated.
If you have edit access to the spreadsheet itself, you should instead consider creating a new column/sheet/etc. in the spreadsheet proper using Google Spreadsheets’s QUERY() function like the first answer suggests that is a subset of your data (in this case, rows whose date is within the last 30 days), and then use this plugin simply to call the appropriate ranges/sheets for the subset you’re interested in, as you’ve already been able to successfully do.
Note in particular that the shortcode’s query attribute simply passes along its value to the retrieval URL as described here, whereas a =QUERY() formula inside a Google Spreadsheet is a proper Google Sheets function. These two things of similar names do not offer the same functionality.
