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You will need to go through a procedure that covers all the bases of setup of recording.
That procedure ends, of course, with the pressing of F3 (Track Mix Mode), then the pressing of
which is followed by pressing the Track Status button repeatedly until the right track is selected for recording to, and its indicator turns red to show it is Ready for recording.
And, to make sure, that the recording media has
1. space enough to record on, and
2. if a memory card, not write-locked, which prevents recording.