Do you see an error message saying that you are not in an eligible region to install Spotify or another skill that you want?
Follow the following steps:
Change your Amazon account to another region:
Go to Amazon.com:
Click on the menu: Your Account: Account > Digital Content and Devices > Devices and Content.
Click on preferences: (to access skills in another region)
In settings - devices/region: Change your address to an address in another region where the skill is available, e.g. Brazil. Click update.
Now just access the Amazon Alexa application, log out and log in again.
This process works for any skill that is not yet available in our country, and that is already available in others.
After installing the desired skills (Spotify and others), you can repeat the process again and change your address to Portugal. The Skill already installed will remain intact.
To install a Skill: (In this case, Spotify)
Enter the Amazon Alexa application; On the bottom bar, click More > Skills and Games > Search for Spotify > Enable to use.
Buy your Amazon Alexa here