I may be wrong but from my understanding, Space X does not have an official API.

[View:https://github.com/r-spacex/SpaceX-API/tree/master/docs#rspacex-api-docs]

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This is not a valid URL. What you have added is just a base URL. In order to get something from it, you will need to add a relative path like this. 
api.spacexdata.com/.../launches

"Not working" can mean so many things. Do you mind getting a bit more specific?