You may have the CTCSS privacy code function enabled on one radio and not on the other. This function keeps your radio's received muted unless it receives a signal from another radio using the same privacy code. If you have Privacy Codes set for radio A but not for radio B you will still be able to transmit from A to B but when you transmit on radio B your signal will not be heard on radio A.
Make sure that both radios are set to the same privacy code or that the function is turned off on both radios.
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