Filtering a report via REST API

I have a report of the format https://xxx.quickbase.com/db/xxxxxxxxx?a=q&qid=xx. I would like to consume this using the REST API, but only select the relevant records using a query. I noticed that you can supply a query using the web ui of the form https://xxx.quickbase.com/db/xxxxxxxxx?a=q&qid=xx&query={xxx} and it shows the result of the report returning only the rows selected by the query. However, if I try to access a similar url via the REST API, for example https://api.quickbase.com/v1/reports/xx/run?tableId=xxxxxxxxx&query={xxx}, I get the following error:-

HTTP request parsing failed with error: "Malformed URI: /api/reports/xx/run?tableId=xxxxxxxxx&query={xxx}"

I have checked and I am not sending "&" so that is probably being converted from the server side.

Is this a possibility, or am I going to have to instead send a series of separate table queries and construct the final result?

------------------------------
Chris Hills
------------------------------