Installing Odoo Modules

When installing a 3rd Party Module, there is a step of steps you should follow from Odoo

You can find those steps here
https://www.odoo.sh/faq#how_to_submodules 

This link says:

A git submodule allows you to integrate other Git projects into your code, without the need to copy-paste all the code (in short).

Required before starting: a Git repository containing some Odoo modules. It can be some apps from the Odoo Apps store or some community modules.

Private repositories

Github private repositories require a few more steps in order to configure properly your submodules. They ensure that Odoo.sh will be able to fetch your private code.

1. Go to your Odoo.sh project Settings then look for the Submodules section.
2. Paste the URL of your sub-repository (eg: git@github.com:USERNAME/REPOSITORY.git) and click on Add.
3. Copy the Public key (it should look like ssh-rsa some...random...characters...here...==). We currently support ssh-rsa and ssh-ed25519 keys.
4. Go to your sub-repository Settings page on Github then look for the Deploy keys tab.
5. Click on Add deploy key and paste the public key into the Key field. You can add "Odoo.sh" as title and save.
6. Now follow the steps described hereunder for the Public repositories.

Public repositories

Here are the steps to add your sub-repository as a submodule of your Odoo.sh project (you don't need to set up a deploy key for public repositories).

1. Let your project "know" that you require a submodule: git submodule add -b BRANCH git@github.com:USERNAME/REPOSITORY.git PATH.
2. Commit this change and push it: git commit -a && git push -u origin master.
3. Wait while Odoo.sh builds your project... and it's done!

There is a good video online about how to do it.
https://youtu.be/vsqzfA3ERD8?t=1182

Please note that some users try just using the "Import" button to import the module, but this will not work.