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 }
 ```
 
+### ICCID
+
+The structure of an ICCID according to the International Telecommunication Union
+should be:
+
+![IccidSchema](./docs/fig1.png)
+
+This gives the structure:
+
+`ICCID = MII + CC + IIN + IAIN + C`
+
+Example Onomondo SIM:
+
+`ICCID = 89 + 45 + 73 + 0000271204 + 3`
+
+### API Response
+
 The API will return different status codes based on different scenarios:
 
 | StatusCode | Explanation                                                                                                                                      |
 | ---------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |
 | 200        | The request was successful and you should get the most recent data from our database. If data is older than 5 minutes, new data will be fetched. |
-| 400        | Bad request. The request parameters didn't validate. Either not a valid iccid or from a not supported issuer.                                    |
+| 400        | Bad request. The request parameters didn't validate. Either not a valid iccid or from an issuer that we don't support.                           |
 | 404        | Not found. The SIM doesn't exist in the issuers API. This response will be cached for 30 days.                                                   |
 | 409        | No information about SIM in cache. Try again later, and you will get either a 404 if the SIM doensn't exist or 200 with data.                    |
 | 500        | Internal Error.                                                                                                                                  |
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