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On a friend's gravel bike, the shifter below - no clicks when the shift lever is flicked.
Nothing obvious with the cable.... thinking it may be broken/stripped ratchet inside? Any idea/suggestions? It most likely explodes in a pile of springs if I open it, so probably looking at a replacement if not an easy fix.

its not a left hand dropper lever is it?
Had similar on a SRAM rival shifter, turned out to be a bit of metal within the housing had broken.
I bought a cheap replacement from planet x, still have them, and still dirt cheap.
https://www.planetx.co.uk/i/q/GLSRRI22XYZ/sram-rival-11-brake-lever--shifter
Cheers, it's hydraulic though, the Planet x ones are all mechanical, unfortunately.
I had that problem. The cable spool which holds the nipple in place broke. SRAM don't sell the part so I thought I would have to buy a new shifter (£££). So I epoxied the cable in place and that worked for a year.
And then I discovered this, which has been a perfect and excellent value fix, so I highly recommend it: https://ratiotechnology.com/product/cable-spool/
Quite a pleasing job to fix, too.
Edited to add: mine was a SRAM Force 1x shifter.
Nice one, ta. That sounds very much like the issue, and that fix is about 10% of the cost of a new lever - much appreciated
https://ratiotechnology.com/product/cable-spool/