The 6th edition of the Publication manual of the American Psychological Association calls for journal articles with DOIs to be formatted with the DOI preceded by doi:, for example

Herbst, D. M., Griffith, N. R., & Slama, K. M. (2014). Rodeo cowboys: Conforming to masculine norms and help-seeking behaviors for depression. Journal of Rural Mental Health, 38, 20–35. doi:10.1037/rmh0000008

In 2012, the APA updated these recommendations in the //APA Style Guide to Electronic References// and now prefers linking dois through a resolver, for example

Herbst, D. M., Griffith, N. R., & Slama, K. M. (2014). Rodeo cowboys: Conforming to masculine norms and help-seeking behaviors for depression. Journal of Rural Mental Health, 38, 20–35. http://dx.doi.org/10.1037/rmh0000008

The APAStyle blog post (where these examples are drawn from) explains these changes in more detail. Instead of the dx.doi.org resolver, the APA style provided by the Citation Style Language (CSL) and used in Zotero uses doi.org, so that the above citation would be:

Herbst, D. M., Griffith, N. R., & Slama, K. M. (2014). Rodeo cowboys: Conforming to masculine norms and help-seeking behaviors for depression. Journal of Rural Mental Health, 38, 20–35. http://doi.org/10.1037/rmh0000008

This resolver is prefered by doi.org, will be recommended by CrossRef in the future and is functionally equivalent to the longer (and older) version. In direct correspondence with the CSL team, APA experts agreed with this modification and provided the following response:

This DOI world is constantly changing, and APA formulated its guideline to use the http://dx.doi.org prefix based on the recommendation of CrossRef.org. CrossRef still specifies that this is the format to use; I am unaware as to whether they know that the doi.org site suggests a simpler format. Certainly as long as the DOI resolves you have satisfied the purpose of the reference, and in the future I wouldn’t be surprised if all publishers officially endorsed the shorter form. In the meantime, if you want to be a stickler for the rules, the dx.doi format is the one that’s officially endorsed.

Best regards,

The APA Style Expert Team