From March 2017, the APA style editors are recommending the latest DOI format, as recommended by Crossref.

This new new format looks like
https://doi.org/………
(the Library’s APA style pages are updated to this now)

You may recall the old new format, that looks like
http://dx.doi.org/……..

Or the old old format, that looks like
doi:…………..
(and this is what EndNote will output with the APA output style “out of the box”)

All these formats are still valid, so the main thing to tell students is to use one format and stick with it within an assignment.

Link to the posting on the APA Style blog announcing this change.