The customer who browses on mobile and buys on the computer: one cart for all devices

A customer looks at your products on their phone on the way to work and adds three to the cart. In the evening they open the computer to pay at their leisure. The cart is empty, or it has a product they added two weeks ago. They might search for the products again. They might not.

Shopping across several devices is the norm: people discover on mobile and pay wherever is most convenient. If the cart does not follow the customer, every change of device is a chance to lose the sale.

Why it happens in PrestaShop

PrestaShop ties the cart to the browser session, not to the customer. When the customer is logged in on their phone and on their computer at the same time, each device can end up with its own cart. What they add on one does not show up on the other.

There is an option, “Re-display cart at login”, which recovers the customer's last cart when they log in. It helps, but it has limits: it only acts at login, and only if the new session does not already have a cart. If the customer was already logged in on both devices, it solves nothing.

Which sales are lost

• The cart that “disappears”: the customer thinks they have lost it and does not bother to rebuild it.
• The half order: they pay on the computer for what was there and forget what they added on the phone.
• False abandoned carts: the phone cart is left abandoned even though the customer bought on the computer, and they get a reminder about something they have already paid for.
• Outdated tabs: the customer has the store open on the computer, adds something from the phone and pays on the computer with an old cart on screen.

What unifying the cart means

The solution is for all the customer's sessions to use the same cart. Not copying products from one device to another, but having both write to the same one. That way what they add on the computer is already on the phone, without waiting for anything.

It only works with logged-in customers: it is the account that links the devices. A guest has no shared identity between their phone and their computer. It is one more argument for making login quick and easy in your store.

The tricky cases

Two carts that already exist

This happens when the customer adds products before logging in and then logs in, or when two devices create a cart at the same instant. They have to be merged without duplicating: if the same product is in both, decide which quantity remains (the larger, the sum or the main cart's), rather than adding it twice.

Old carts

Dumping something the customer added two months ago into today's cart fills it with things they do not remember. It is better to offer those old carts separately, with photo and amount, and let them decide whether to add them.

Products that can no longer be bought

When merging carts, an out-of-stock or disabled product must not slip into the shared cart, nor disappear without explanation.

Vouchers, gifts and customisations

Vouchers with a code and customised products have to travel with their data. Gifts from a voucher must not be copied as paid products: the voucher will add its own again.

Negotiated prices

In assisted or B2B sales, a sales rep may prepare a cart with a special price and send it to the customer. That cart must not be mixed with others, neither to receive nor to give products: the negotiated price has to be respected.

Simultaneous requests

If two tabs merge carts in the same second, without a per-customer lock quantities can be added twice.

After the order

As soon as the cart becomes an order, the other device should be left with an empty cart, and the customer's next cart is shared again. Nobody wants to see on their phone the cart of a purchase they have already paid for.

How to measure whether it affects you

Before changing anything, look at your data:

• What share of your logged-in customers come in from more than one type of device?
• How many abandoned carts belong to customers who bought shortly afterwards?
• Do you get complaints along the lines of “my cart has been wiped”?

If you sell a lot to repeat customers with accounts, it probably affects you more than it seems.

Frequently asked questions

Does it affect abandoned cart reminders? It should improve them. A cart that has been merged into another has to be left empty, not deleted, so as not to trigger reminders about something the customer still has in their shared cart or has already bought.

And in multistore? Each store has its own carts. If a group of stores shares customers and orders, it makes sense for the shared cart to belong to the group.

What happens to the customer's data if they ask you to delete it? The history of merged carts is one more piece of personal data: it has to be deleted along with the rest when you remove the customer.

Compatibility

Unifying the cart touches the start-up of every request and the checkout. Choose a solution that does not use core overrides and that works with your version of PrestaShop and PHP; if your store is on an old version, test it first on a copy and take the opportunity to consider upgrading.

How to solve it in PrestaShop

RKR Carrito Único makes all the sessions of a logged-in customer use the same cart, on the computer, the phone and every tab, without having to enable “Re-display cart at login”. Open pages check every 20 seconds (adjustable or can be switched off) whether the cart has changed, only while the tab is visible. It merges carts that have split without duplicating, with the quantity rule you choose and a per-customer lock; vouchers and customised products travel with their data, out-of-stock products do not slip in, old carts are offered separately and carts with a negotiated price are never mixed. After the order, the other device is emptied automatically. No overrides, from PrestaShop 1.7.8 to 9.x, and multistore.