No VPN at those sites I’d bet, that’s the point of the panel feature.
Router A: you can’t switch that from Hermetry, by design. “Allow panel access from my cloud account” is the router owner’s local consent and lives only on the router’s own Cloud page. Someone on site has to turn it on once. We had a farmer do it with me on the phone, it took five minutes: log into the router’s local panel from a laptop on the LAN, Cloud page, tick the switch. After that Open panel works from anywhere.
Router B: the firmware is too old for panel sessions. Update it through Hermetry’s firmware page. For a router that far away I’d do it on its own first, not as part of a wave, and check its Firmware tab for the Updates over LTE setting if it’s on the mobile uplink. Licensed devices have local approval and metered-link rules, so it may sit in Waiting until those allow it.
Couple of things for when it works. If the router is on LTE you get a confirm that the session may use up to 50 MB and is then closed. Sessions end after 30 minutes without use or 4 hours total. Only the person who opened a session can enter it, so a colleague opens their own. And what you change inside the panel is up to you, opening it changes nothing.
All the refusal messages are listed on Remote access to a router’s panel.