A method I have used in the past to repair chips with quite good success was to use grout and mitre glue.
I would find a grout as close to the tile colour as possible (can mix different shades) then using a Stanley blade put a tiny coat of mitre glue onto the chip. Next sprinkle the grout over the glue and push it in with the blade, put on more glue then grout until slightly proud, compacting it with the blade each time. Once done can use the activating spray to set it off. Then using either a brand new blade or fine grit sandpaper get the repair flush with the tile. Will stick like sh*t and should be water resistant. Hope this helps anyone 👍