According to the APA's web site,
A is a unique alphanumeric string that identifies content and provides a persistent link to its location on the internet. DOIs can be found in database records and the reference lists of published works.
Note: In APA style (7th edition), the DOI number is required to be represented as a clickable link. More recent DOI numbers are typically already in clickable link format (such as in Example 2 above). If, however, the DOI you are citing is not in link format (as in Example 1 above), you must convert it to a link by doing the following (as shown below using the DOI in Example 1 above):
To convert a non-link DOI to a clickable link: