What it says on the tin, have the “sell to vendor” button in the inventory both on the top and bottom of the page. If you have a lot of stuff it really stretches the page and on mobile it’s fairly inconvenient to have to scroll all the way back up.
While I think this may be a quick band-aid sort of fix, I think in general the inventory page needs a serious overhaul, including the vendor-selling functionality. The placement of the button, the limit to only sell 100 maximum at a time (what am I supposed to do with my 24k candles?! Sell them 100 at a time 240 times?!) So yeah, support for this as a temporary fix, but in the long run, the page needs bigger fixing.