Subreport to add a new page per Main report item

I need to add a Subreport to the Remittance Advice form, so that AFTER the main report, an additional page is added per Bill line from the main report, with details of each Bill.

I have created a form for the Bills, moved some items from the subreport report header to a group header, and linked it to the main report via a subreport in a new ReportFooter section (to ensure it prints AFTER the main report, not within it).

I am seeing all the correct data per Bill loading as expected, but the it is all stacked on a single long additional page, with no page breaks between each Bill group. I've tried toggling various PageBreak and KeepTogether properties in the Main and Sub reports but cannot get the subreport to split out per Bill.

I took another approach to use a subreport for the top level main report, then promoted the subreport data to the main report, still using some subreports for ease of grouping and display, but this allowed me to add page breaks to the main report, in the correct places, therefore getting what I needed, a new page per subreport record.