Apple server side migration (Importing Receipts) always failing

Hello, 

I am trying to migrate Apple's subscriptions via client-side (I have all data required) to RevenueCat, however, I keep receiving the status 400 (Bad Request) from the REST API POST /receipts endpoint.

This is an example of format that I am sending:

1{
2  app_user_id: 1,
3  product_id: 'pro_quarterly',
4  fetch_token: 'MIIUCwYJKoZIhvcNAQcCoIIT...jcxwb5vocU=',
5  price: 13.99,
6  currency: 'USD',
7  attributes: {
8    '$displayName': { value: 'Jhonatan' },
9    '$email': { value: 'jhonatan@gmail.com' }
10  }
11}

I have been succefull with Android's migration, unfornately I do not know what I am doing wrong or if there is something missing with the Apple's migration.

All products from Apple are registered in RevenueCat's dashboard, App Store Connect App-Specific Shared Secret is set, as well the authorization header with the public api key refering to RevenueCat's IOS app project.