First, the Express has a single band WiFi radio, so if your router is only broadcasting on 5 GHz, you need to enable the 2.4 GHz radio. The next thing is the channel number. The 2.4 GHz band has channels 1-14, but the top three are not permitted in North America so Roku devices will not see them. The best channels to use on 2.4 GHz is 1, 6 or 11. These are the only three channels that don't have overlap with each other. Most routers are set to auto-select the channel, so you may need to set it manually.
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