If I remember correctly, project online uses oData version 3 which doesn't support now() for dates.... enter powerquery/BI. Took me a long time to come around to trying this... but you can craft the URL string using M code / power query and then make the odata call.
Here's an example of grabbing base capacity from the odata filtered ResourceTimephasedDataSet
Key is in correct formatting of the date and the single quotes that wrap it.