How do you reduce cart abandonment?

Show the total earlier. Most abandonment is not indecision, it is a delivery cost or a delivery date that appeared after the customer had made up their mind.

What decides it

Rank the fixes by what they cost you: shipping cost visible on the product page, delivery date before checkout, guest checkout, wallet payment. A recovery email is worth having and it is the last line, not the first.

The part that gets skipped

Discounting to grow trains customers to wait for discounts. It works once and costs afterwards.

Traffic is the expensive problem and conversion is the cheap one. Doubling a 1% conversion rate is usually easier than doubling visitors, and costs nothing per month.

Retention beats acquisition on every measure, and almost every store spends the other way round.

Where an app fits

Push notifications are the one growth channel you do not rent. Every other route to a customer is paid for again each time.