What's likely happened here is that the 'SETID' function on the station is telling the network an incorrect station ID. Essentially the station turns on, talks to the network, says it's a station named ABCD (just as an example) but in the network, the station is looking for something like DCBA, when you 'add station' to add a station to your market.
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To correct this, use the SerialPortUtility tutorial (in the Intercom tool). Then connect the station with USB to your computer, power it on, and send the command:
​SETID:
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Make sure you hit enter to drop the cursor down a line and that the port is opened (there are step by step video instructions in Intercom, just search for SerialPortUtility) and then hit send. That station will respond with SETID:ABCD, if it returns with something blank, strange characters or anything different than the QR code on the physical station you should send the command SETID: and enter the code that's physically on the station.
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You can confirm that it saves the ID by sending SETID: and leaving it blank and it will return with SETID and the correct ID code. Unplug the USB, restart the station and it should then connect.