welcome to GoY

I suspect the heat and the fact it is in direct sun. The breezy warmth will have meant that it hasn't really had enough water.
Move to a less direct sunny spot, and if you can stand the pot in a shallow tray so it as a reservoir of water. The plant may then start new growth. Don't feed it at the moment wait until you see new growth.

I understand it is a tree rather than a shrub. Dont leave it standing in water over autumn/winter as that will probably kill it.

I suspect the fact that it wants to be a large tree and it's in a container might be the problem. Although you water and feed regularly there might not be a great deal of soil in the pot as it will have been displaced by the roots and unable to retain the moisture and feed. I would consider lifting the tree and the rootball and re-planting in the garden.