I’m having the same problem, it’s very hard to use docker when the documentation is giving 503 errors.
There’s nothing on https://status.docker.com/ indicating there is a maintenance window, nor is there any indication that they are aware of the problem.
Please try a slight variation on your URL, i.e. https://docs.docker.com/engine/api This will redirect to a different page https://docs.docker.com/develop/sdk/, where you can scroll down to the API version matrix at https://docs.docker.com/develop/sdk/#api-version-matrix , and choose the version appropriate to your needs.
@bryceryan I think you misunderstood the problem. the servers were giving 503 errors for many of the docs pages. It seems to be fixed now, but some kind of acknowledgement that there was a problem would be very helpful.