Kindle books can generally be referenced like a print book if they have the same text as a print version. If a book is only available on Kindle, reference as below.

Reference list:

Seligman, M. (2011). Flourish: A New Understanding of Happiness and Well-Being. Simon & Schuster. https://www.amazon.com/Flourish-Visionary-Understanding-Happiness-Well-being/dp/1439190763/ref=sr_1_1?keywords=Flourish+seligman&qid=1574807561&s=books&sr=1-1

The citation in your text will be:

(Seligman, 2011)

If you have used the author(s)’ name(s) in your sentence then only the year of publication, with a paragraph reference if necessary, is placed after it in brackets, e.g.

Seligman (2011) suggests that ...

When citing a direct quote, you should use the “page number” feature that Kindle gives which usually matches a print version. If not, use another way to identify a quote’s location (e.g. chapter number, section name). Do not give a Kindle location number.