Build always failing

Hi guys I'm trying a simple step just to login to az through Jenkins but I get the following message:

```
Failure:
Build step 'Azure CLI not found' changed build result to FAILURE
Finished: FAILURE
```

#### What I have done
1. Created an Azure service Principal called `JenkinsPrincipal` and verified it works as I got the following message when clicked "Verify Principal"

```
Successfully verified the Microsoft Azure Service Principal.
```

2. Created a new Multibranch Pipeline and add the following code on the Pipeline script

```
node {
stage('Deploy'){
azureCLI commands: [[exportVariablesString: '', script: 'az login']], principalCredentialId: 'JenkinsPrincipal'
}
}
```

3. Also created a "Freestyle Project" job to test a build step from there but also got the same error as above.

Any thoughts what I'm doing wrong?