Combine Dataset pushed via API with other sources

Hi all,

I may be missing something really straight-forward here, so bear with me...

One of my developers managed to create a new dataset using a push API - he's now updating this every 5 minutes so it's very fresh.

I'd like to use this dataset in my existing reports ideally, but can't seem to Get Data --> Power BI Datasets from my existing report.
When I create a new report I get the data, but then can't add any other sources.

Have I missed something?
Surely this must be possible somehow.

Thanks in advance,

Patrick