Mobile games and foot-in-the-door technique
Footwork on the doorstep
In psychology, kicking on the doorstep is a technique that allows you to agree to a small request before a larger one. It’s a step-by-step psychological technique, as if you’re just slightly shutting the door that’s about to close, and then gradually entering the door. For example, a door-to-door salesperson starts by asking the landlord if he can just walk into the house for a while to demonstrate the product. According to an actual study, if you go from house to house and receive a fundraising, you will receive a simple signature on the petition first, and then visit again a few days later, and the rate of accepting the fundraising is higher. 
Footing techniques in the wallet (…door)
Footing techniques on the doorstep are often used in on-boarding experiences, such as the membership phase of app-web services. For example, shopping mall membership is an example of a shopping mall that requires complex user information, starting with information that requires a small degree of involvement from the user, such as a mail address. When you first sign up as a member of a shopping mall, you can sign up very simply these days by linking portal-social services such as Facebook and Naver. However, when the actual payment time comes, you must enter more complex personal information such as the address to be delivered and card information for payment. If you have to enter this personal information from the beginning, you can feel annoyed and psychological rejection, so you can step up your involvement. But pay-to-win (Free-to-play)  gaming services and sample marketing can be seen as similar strategies.
Mobile games and wallet footwork techniques
A closer look at the free-to-play (but-pay-to-win) game service, especially the In App Purchase , shows that the footing technique is more cleverly applied to the doorstep. It’s not a doorway, it’s a design technique that steps into your wallet.
1. a low-priced product
The role of the lowest-priced product, such as starter bundles, is especially important in games that induce users to make light payments, such as mobile casual games. Starter Bundles are usually the cheapest and most efficient of all bundled products, *designed to pay only once per user. In the case of casual games, it serves as a bait product that induces users to take the first step in in-app payment lightly through a starter bundle and gradually pays for more expensive products after the product disappears after payment.
In order 1. Wildscapes (Playrix) / 2. GardenScapes (Playrix) / 3. DreamBlast (Rovio) / 4. ToonBlast (Peek Games)
2. Step-by-step product design
You can also step into your wallet in a more persistent way than the starter bundle. The popular casual running game Cookie Run: Oven Breaks sells a special package to celebrate updates every month on a regular basis. This product is designed in a total of three stages, and in the first stage, you can pay for the product virtually free of charge for just two crystals . If you pay, you’ll get 200 crystals, more than 100 times the amount consumed (…)i) Immediately after the user pays for this first-stage product, the second-stage product is exposed, which consists of three products priced from KRW 3,900 to KRW 12,000. The price of goods is getting higher. And the last three-step product will be exposed to the user who paid for all three products.
Cookie Run: Special Package to commemorate the update of the oven brake
Meanwhile, the casual puzzle game Jam City attempts to step into the user’s wallet in a similar way. Most coin consumption in casual puzzle games occurs on the succeeding paper . Cookie Jam exposes a three-step product that is targeted at users who have given up on continuing purchases. When the user first gives up on continuing, it exposes the most efficient, low-cost bundle of 2,800 won. And the user who paid for this product will be exposed to the second product, the Move Tribe Bundle of 12,000 won, and the user who paid for the second product will be exposed to the Move Tribe Bundle of 25,000 won. If the user decides not to buy the products of each stage, the user will persistently induce payment by exposing the relatively inexpensive products of the previous stage again in the case of the user’s next abandonment.
Cookie Jam’s Continuation Paper Bundle
3. Reverse product price sorting
There’s also a way to step into your wallet in a more subtle way. In the mobile casual puzzle game, Gardenscape (Playrix), a store UI that had been sorted from cheap to ascending, cleverly encourages users to pay for higher-priced products by changing their sorting priorities from expensive to descending. This design can also be found in other casual puzzle games of the same genre, such as Peek Games, and is a good example of anchoring effects.
It’s like a combination of two psychological techniques.
From the perspective of the KPI of the mobile game, the wallet kicking technique is a strategy to increase the ARPPU  after solidifying the payment user base by increasing the PUR  and ARPDU . However, before using these techniques, you must first consider whether the game you have developed gives users the pleasure to pay for and whether you have designed the product to make them feel positive about their post-payment experience.
1. Provide inexpensive and efficient products so that users can easily start paying for the products.
2. Design products to gradually pay higher amounts of products using step-by-step product design or store UI alignment method.
3. Don’t forget that the most important thing is the fun of the game and the user experience after payment.
 Evil Design (Chris Nordzer, Wikibooks, 2014)
 Partially Paid Service Method
 Paying in cash through platforms such as iOS and Android within an application
 a kind of money used in a game
 In the puzzle game genre, the opportunity for a user to manipulate a block is collectively referred to as Move, which allows the user to pay in-game currency (ex) and receive additional opportunities through the following page when the user is in crisis of game over.
 PUR: Paying User Rate (percent of all users who made cash payments)
 ARPDAU: Average Revenue Per Daily Active User
 ARPPU: Average Revenue Per Paying User
[*] Please refer to my other post about the store star request pop-up of the app, which is also an example of footing technique on the doorstep.
*Original source: https://brunch.co.kr/@jaehyunkim