Simply set up NAT rules on hEX to access the RB260.
Nothing in the initial description is clear,
so it's impossible to be more specific.
I don't see VLANs anywhere, and VLANs aren't required to access the configuration.
The solution was to use a vlan for switch management (vlan99). The stumbling block, no internet access, required a vlan 1 to be setup and assigned to the router and ont ports on the switch. Normally, this is not a requirement.