If the Mayfly reports “could not wake modem for clock sync” then that means there’s no communication between the Mayfly and the cellular module. That usually happens when then cell module isn’t properly seated all the way in the Bee socket or the pins aren’t aligned properly. If the bee module is correctly installed, the clock sync part of the sketch is purposely made long (2 minutes) to give a newly activated SIM card time to join the network for the first time. I don’t know how US Cellular is, but with our Hologram cards, it can sometimes take several tries of doing the 2-minute sync session to get the card to join the network for the first time. Once it’s done that, subsequent connections can happen in about 5 seconds. So if you’re in an area with weak or no US Cellular signal, then it might be challenging to get that initial connection completed. If your cell data plan supports things like tablets or phones, then you could put the new SIM card in a different device that is constantly on and use that to establish the card with your provider first, and then move it back to the SIM7080 after that. And if US Cellular doesn’t recognize the SIM7080 as an approved device for their network (which is what Verizon does), then it probably won’t let the Mayfly connect at all. That why we’ve been using the Hologram network for the past 6 years because they’ve supported all of the various cell modules we’ve ever tried to use, and for around $5 per month per device.
What antenna are you using? There’s 2 small antennas that come with the SIM7080 board (one’s for cell, the other for GPS and not currently used), but we’ve found that the small cell antenna is usually not sufficient unless you’re in an urban area or very near a supported cell tower. We’ve had much better luck with a larger antenna like the one suggested in section 6.1 of the manual: https://www.envirodiy.org/knowledge-base/building-an-envirodiy-monitoring-station/