API documentation
2018/12/14 (v1.4)

Make a GET request to: 

Possible responses for all actions 
BAD_API_KEY (Status code 403) - there is not a valid key parameter
SERVER_ERROR (Status code 500) - there is a server error
BAD_ACTION (Status code 400) - action is not on the below list

Actions list

Extra input: None
Response: The date that the ICCID was last changed, in UNIX timestamp*
Since: v1.0

Extra input: None
Response: The date that the current ICCID was last verified to work, in UNIX timestamp*
Since: v1.0

Extra input: None
Response: NO_ICCID, or the current ICCID
Since: v1.0

Extra input: &iccid=<ICCID> (the ICCID to check)
Response: IS_CLOSED, NOT_CLOSED, or UNKNOWN (Since v1.4 2018-12-14)
Note: This only works for ICCIDs that you got through this API or site (i.e. you can't ask it to check random ICCIDs). 
Since: v1.0 (IS_CLOSED, NOT_CLOSED), v1.4 2018-12-14 (UNKNOWN)

Extra input: None
Response: "OK" if the server is working, or "CHECKER_ERROR" if the ICCID checking server is unresponsive
Since: v1.2 (2018-09-17)

* UNIX timestamp = seconds since 1970/1/1 00:00 GMT