I have my payment

I have my payment gateway set up and on live. The settings are all there for it to direct to Paypal

When the user signs up after entering their details they get a message they have registered but it does not take them to Paypal to pay - to pay they have to go to their membership, click on the invoice number and then hit the subscribe button

Why does it not take them to Paypal automatically so they subscribe during the registration process?