What is a DOI?
Answer
DOI - Digital Object Identifier. A DOI is used to identify an article or eBook and it never changes, so it is more reliable and permanent than a URL.
Most online journal articles and some textbooks have DOIs. If a resource has a DOI, it must be included in its reference.
Here are the examples of DOIs:
https://doi.org/10.7810/9781988587189 OR doi: 10.1111/jscm.12006
In your reference list, you must use the first format (https://doi.org/10.7810/9781988587189). You can turn the second format into a URL by removing 'doi:' and replacing it with 'https://doi.org/' (in this case https://doi.org/10.1111/jscm.12006).