I use the tip that is slanted and flat in the middle at the highest temp. The flux and solder I used was the ones that's in this kit
https://www.amazon.com/gp/product/B08M6L3B4C/ref=ppx\_yo\_dt\_b\_asin\_title\_o00\_s00?ie=UTF8&th=1
I use the flux that's in this kit below. It is HTM Rosin Paste Flux
https://www.amazon.com/gp/product/B08M6L3B4C/ref=ppx\_yo\_dt\_b\_asin\_title\_o00\_s00?ie=UTF8&th=1