With PowerShell, we can use the invoke-RestMethod cmdlet to make Restful API calls to get JSON data. When using the SharePoint Restful APIs, the cmdlet returns the JSON data in string format which is not the intended result.

powershell-sharepoint-invoke-restmethod.ps1

#set the headers content type
$contentType = 'application/json;odata=verbose'
$headers = @{}        
$headers["Accept"] = $contentType    
$headers["Content-Type"] = $contentType   

$uri = "ozkary.sharepoint.com/GetByTitle('LIST-NAME')/items"
$data = Invoke-RestMethod -Method GET -Uri $uri -UseDefaultCredentials -Headers $headers  

#returns string
$data.GetType() 

#ERROR - returns error that there are duplicate attributes 
#(Id, ID) which is the SharePoint default
$json = ($data | ConvertFrom-Json )   

#TIP - this works because we replace ID attribute to a #different name
#it should  parse the string and return a JSON object
$json = ($data.replace("ID","IDTemp") | ConvertFrom-Json )

#we should be able to access the results array
$json.d.results