2 alarms at same address

Hi,I’m a bit confused about ring protect subscription,I live at a small holding and have a ring alarm and doorbell on my house, I also have a home office in a converted barn that I have just put a 2nd ring alarm in, one system set up as “house” and one set up as “barn” I have tried setting up ring protect plus free trial but it only sets up assisted monitoring on “Barn” and when I try to add it to “house” I click I agree, next, it then just goes back to dashboard,I contacted customer care via live chat but was told I would need separate subscription for each system On the ring website it states “ All devices at one address will be covered under Ring Protect Plus plan” Anyone else had this issue and can shed some light on it?Thanks