I suggest you start out by checking that you can run the exampleSite in this repo. I just tested the steps below now:

git clone https://github.com/bep/docuapi.git
cd docuapi/exampleSite
hugo server

If the above works, then your environment is OK, and you can just copy the entire exampleSite folder and adjust the settings/content.

If the above does not work, you need to provide me with whatever error you get, but note.

This theme requires a reasonably new Hugo version (the extended version) and Go installed.

I have the same issue as @kostya-konev, when I setup the server using the following docs https://tw-docs.com/docs/static-site-generators/hugo-api/

When I installed go (brew install go) I am getting empty page when starting the server with hugo server.

I think that the issue is sourced in the go.mod file

For the guys who have the issue in the future for me it worked when I modified the go.mod file with the following content

module github.com/bep/docuapi/exampleSite

go 1.16

require (
	github.com/bep/docuapi/v2 v2.3.0 // indirect
	github.com/gohugoio/hugo-mod-jslibs-dist/alpinejs/v3 v3.21000.20300 // indirect
	github.com/olivernn/lunr.js v2.3.9+incompatible // indirect
	github.com/slatedocs/slate v2.13.1+incompatible // indirect
)

git clone https://github.com/bep/docuapi.git
cd docuapi/exampleSite
hugo server

hugo v0.113.0 failed to start the exampleSite, the error message is

Error: command error: failed to create config from result: failed to decode config for language "en": unknown config key "blackfriday"

After upgrading to hugo v0.117.0 it works now. Maybe it is related to this issue gohugoio/hugo#11159.