Webshop Flow From Quotation to Invoice

Hi Everyone,

I just want to know how webshop flow from the quotation, order and invoicing

My last status order is to pay.

i have pay with payment gateway but is not create invoice automatically?

If payment is done then It will create two entries at once, the first is the sales voice and the second is the payment entry.

in webshop there is any validation for stock?
how if item out off stock is still can be checking out?

If a sales invoice is generated, the stock will be deducted automatically.