DOI stands for Digital Object Identifier. It is a unique address for an online resource, just like a URL.
Many electronic resources (esp. journal articles) have a DOI. The location of the DOI may vary depending on the type of database you are using, however you can usually find the DOI on the first page of the article or database. See below for some examples:
In APA 7th ensure you format your DOI this way (incl. hyperlink): https://doi.org/10.1016/j.mnl.2011.07.013
If the DOI on your resource shows in the old format, as in the examples above, change the DOI as follows:
- Old DOI format: DOI:10.1016/j.mnl.2011.07.013
- New DOI format: https://doi.org/10.1016/j.mnl.2011.07.013 (removing 'DOI:' and replacing it with 'https://doi.org/').