You need to place the modules (extracted) into the apps folder path specified in your config file.
Then restart Odoo service and go to Apps, then click "Update" to get them in the list.
Finally you can then install them.

HI, you can follow this: 

https://youtu.be/AiwKyMVa_jQ

Hope it helps

Hi 

(I) Thanks for the reply, but it didn't work.

Below is how I've done:

1. My addons_path = c:\odoo16\server\odoo\addons

2. I downloaded this free app https://apps.odoo.com/apps/modules/16.0/ecpay_invoice_website/

3. The extracted ZIP file contains two folders, "ecpay_invoice" and "ecpay_invoice_tw"

4. I placed these two folders in C:\ODOO16\server\addons

5. Turned off the browser then started the browser again, then went to: http://localhost:8069/web#action=36&model=ir.module.module&view_type=kanban&cids=1&menu_id=5

6. Clicked "Update Apps List"

7. The app did not show up

9. I've tried with other free apps either and yet they could not show up.

What have I missed or done wrong? What extra information do I have to offer to get help?

(II) I've seen others that can find third party apps in the Apps page and do not need to download via apps.odoo.com. How did they do that?

Hi,

Locate Odoo Addons Path from Config File:

• Open your Odoo configuration file (usually named odoo.conf).
• Look for the addons_path setting, which specifies the path(s) where Odoo looks for modules. It might look like this:

  ini

• • addons_path = /path/to/odoo/addons,/path/to/your/modules
    

• Extract the Module Zip File:
  • Extract the contents of the downloaded module zip file.
• Copy the Module to the Specified Path:
  • Copy the extracted module folder or files into the directory specified in the addons_path setting.
• Restart Odoo Server:
  • After copying the module, restart your Odoo server to apply the changes.
• Update Apps List:
  • Go to the "Apps" page in Odoo and click on the "Update Apps List" button. This will refresh the list of available modules.
• Install the Module:
  • Now that the module is in the specified addons path, you should be able to see it in the list of available apps on the "Apps" page.
  • Find your module and click on the "Install" button to install it.

Hope it helps