Looking on the internet deeply has found these results:

in more detail is the most popular phrase on the web.

in more details 133,900,000 results on the web	in more detail 188,100,000 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
It doesn't look like this phrase is very popular! The search could not find any examples on the internet.	This should be looked at in more detail. Nevertheless, I would like us to discuss the energy issue in more detail. Let me address trade issues in more detail. However, I should like to speak in more detail about the crisis and young people. B85M describe the elements of the definition in more detail. Section 6.3 discusses the internal organisation of the ESAs in more detail. Paragraphs B85B The above concerns are set out in more detail below.

in more details

133,900,000 results on the web

in more detail

188,100,000 results on the web

More popular!

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

This should be looked at in more detail.
Nevertheless, I would like us to discuss the energy issue in more detail.
Let me address trade issues in more detail.
However, I should like to speak in more detail about the crisis and young people.
B85M describe the elements of the definition in more detail.
Section 6.3 discusses the internal organisation of the ESAs in more detail.
Paragraphs B85B
The above concerns are set out in more detail below.