Anchor Line to Anchor Buoy

On a single-line array, the anchor line continues past the butterfly knot and the connection point to the growline, and can be tied directly to the anchor buoy.

The anchor line continues past the butterfly loop to attach to the anchor buoy with a bowline or anchor knot.
This video shows how to connect the anchor buoy to the end of the anchor line with a bowline knot.

An alternative setup is to splice a loop at the end of your anchor line and use a short pigtail to connect the anchor buoy to the anchor line.

Here the anchor buoy is connected to the anchor line with a short connecting line.