When you want to offer prepaid amounts that customers can purchase upfront and use over time, you can implement a prepaid system. Popularized by companies like OpenAI, this has a number of advantages, like committing customers to a certain usage, and getting paid upfront for services.

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Example case

In this example, we have a video transcription service that offers
  • 10 minutes of free transcription
  • Customers can purchase additional minutes in packages of $10 per 60 minutes.
  • The packages will have tiered pricing: if they purchase more than 300 minutes, the additional minutes will be $5 per 60 minutes.

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Setup

Let’s create our products. We’ll create our base free product and our prepaid package product.

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Base Product

Included usage will be set to 10, for 10 minutes of free transcription. Since our free minutes don’t refresh (eg, it’s not 10 minutes per month), we set Reset Interval to “no reset”.

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Top-up minutes Product

Now we’ll create our top-up minutes product. We’ll set the included usage to 0, and again set Reset Interval to “no reset”. We’ve added a tiered price for the top-up minutes and importantly set the “usage is prepaid” flag. This tells Autumn to expect a quantity to be sent in when a customer attaches this product.

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Implementation

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Checking if they can transcribe

Whenever our user wants to transcribe a video, we’ll first check if they have enough transcription-minutes left. 
curl -X POST "https://api.useautumn.com/v1/check" \
-H "Authorization: Bearer am_sk_1234567890" \
-H "Content-Type: application/json" \
-d '{
  "customer_id": "john-yeo",
  "feature_id": "transcription-minutes"
}'

{
  "customer_id": "john-yeo",
  "feature_id": "transcription-minutes",
  "code": "feature_found",
  "allowed": true,
  "balances": [
    {
      "feature_id": "transcription-minutes",
      "required": 1,
      "balance": 10
    }
  ]
}
Autumn automatically created our customer and assigned them the base product.

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Using up minutes

Now let’s implement our usage tracking and use up our minutes. 
curl -X POST "https://api.useautumn.com/v1/track" \
-H "Authorization: Bearer am_sk_1234567890" \
-H "Content-Type: application/json" \
-d '{
  "customer_id": "john-yeo",
  "feature_id": "transcription-minutes",
  "value": 10
}'

{
  "id": "evt_2w5dzidzFD1cESxOGnn9frVuVcm",
  "code": "event_received",
  "customer_id": "john-yeo",
  "feature_id": "transcription-minutes"
}
Since we’ve used up all our minutes, if we call the check route again, we’ll get allowed: false. We can use this to prompt our user to purchase a top-up.

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Purchasing a top-up

For our top-up flow, when a customer clicks “purchase” and chooses a quantity, we’ll use the attach route to get a Stripe Checkout URL for them to make a payment. 
curl -X POST "https://api.useautumn.com/v1/attach" \
-H "Authorization: Bearer am_sk_1234567890" \
-H "Content-Type: application/json" \
-d '{
  "customer_id": "john-yeo",
  "product_id": "top-up-minutes",
  "quantity": 420
}'
In this case, the customer chose 420 minutes, so they should be charged:
  • 300 minutes at $10 per 60 minutes = $50
  • 120 minutes at $5 per 60 minutes = $10
So the total charge is $60. Once our customer pays, we can see they have an additional 420 minutes available from the top-up product. The customer can now use more transcription minutes, and top up again if they run out.