Not really much else to say - I know this has been brought up in the past, but it still isn't fixed.

Make sure that you have Critical Role Content toggled ON (red/right) in your character's preferences.

If you still don't see Sapping Sting as a learnable cantrip for your Wizard, is it possible that you don't have access to Explorer's Guide to Wildemount? Even if you had access to it before and were able to select the Chronurgy subclass then, you won't be able to add spells from that sourcebook if you don't currently have access.

Critical Role content is turned on and I didn't buy EGtW, but I did purchase all the spells from it. I primarily play spell casters, so I've bought out the spell sections from a lot of those books.

actually, correction, I went back to double-check and it looks like I thought I purchased them because the individual spells weren't showing, but I guess that's just because you can't purchase those spells individually, only as a bundle. I purchased the bundle and now it's there. thanks!

That's odd, you should be able to purchase individual spells in the Individual Purchase Items section below Spells; but I'm glad you have the spell now :)

I have both Taldorei Reborn and Explorer's Guide to Wildemount. But I can't add Sapping Sting to my Blood Magic wizard

Quote from Belrevan1986 >>

I have both Taldorei Reborn and Explorer's Guide to Wildemount. But I can't add Sapping Sting to my Blood Magic wizard

Sapping Sting and all other Dunamancy spells are specifically limited to the Chronugist and Graviturgist sublcasses found in Explorer's Guide to Wildemount.. 

I have this issue too - can it be fixed?

Many thanks - where do I make a home brew spell?

Collections > Create Spell