I'm experimenting with some hooks, but which one should I use to trigger an action when the client presses the submit button on checkout page?

I'm trying to add a QR for each Order, so when the client goes to the place to get his product, the shop scan the QR and that order puts in a 'completed' status.

I'm using the `woocommerce_thankyou`, but is the best hook action to do it?