Shure Microflex Wireless User Manual page 78

Software
Link Microphones
Up to two microphones can link to each audio channel,
though only one is on air at-a-time. Use the secondary link
slot to add a microphone for battery redundancy or flexibility
during events.
① Link Slot Selection
Up to two microphones link to each audio channel using the
primary and secondary link slots. The secondary link slot is
useful for an additional or alternate microphone that can be
prepared before the event.
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② Link Button
Links microphones in the charger to audio channels.
③ Cancel Button
Cancels the link procedure.