Yes, I agree with Mika.
Soldering Flux!
The most successful soldering I have ever done is with liquid soldering Flux.
I use DCC Concepts, No-clean sapphire flux and Sapphire solder. Both excellent products.
If Little Bird can get DCC concepts soldering products at wholesale and re-sell at the same price (or better) then we can add solder and flux to our next hardware order!
ps. I think DCC get their own brand of products manufactured for them. Maybe you can investigate Little Bird Electronics branded Solder and Flux
Thanks Maddy