PayPal is only available for one-off orders. 

Paypal is not available as a payment option at checkout if you have either of the following in your basket:

• you had selected Subscribe & Save for one of the items in your basket, or 
• if you have selected to join the Food Explorers Club membership with your order.

Both of these involve setting up future payments - either regular deliveries of the Subscribe & Save item or an annual membership fee payment.  This cannot be done with PayPal.

So if you have opted for either of these features you will not see PayPal as a payment option at checkout - instead you must choose Card payment, or Apple Pay, or Google Pay.