According to kaggle api documentation the location where credentials json is looking for is ~/.kaggle/kaggle.json as google colab environment is Linux based. In your snippet you try to config path parameter, but it is not used to looking for credential json:

- path: Folder where file(s) will be downloaded, defaults to current working directory

So the full working snippet for google colab environment would be:

!mkdir ~/.kaggle
!touch ~/.kaggle/kaggle.json

api_token = {"username":"username","key":"api-key"}

import json

with open('/root/.kaggle/kaggle.json', 'w') as file:
    json.dump(api_token, file)

!chmod 600 ~/.kaggle/kaggle.json

And then some api call like

!kaggle datasets download -d datamunge/sign-language-mnist

Basically, if you want to use the Kaggle python API (the solution provided by @minh-triet is for the command line not for python) you have to do the following:

import kaggle

kaggle.api.authenticate()

kaggle.api.dataset_download_files('The_name_of_the_dataset', path='the_path_you_want_to_download_the_files_to', unzip=True)

I hope this helps.