SideLoadinf feature is not enabled on the site in SharePoint online

Error: Error occurred in deployment step 'Install app for SharePoint': Sideloading of apps is not enabled on this site.

I was trying to deploy a app in to SharePoint Online, then i got above error.

Solution: I have enabled Sideloading, then it resolved my problem.

Open: sharepoint online Management Shell

Copy below script and paste it sharepoint online Management Shell.

	#CODE STARTS HERE
	$programFiles = [environment]::getfolderpath("programfiles")
	add-type -Path $programFiles'\SharePoint Online Management Shell\Microsoft.Online.SharePoint.PowerShell\Microsoft.SharePoint.Client.dll'
	Write-Host 'Ready to enable Sideloading'
	$siteurl = Read-Host 'Site Url'
	$username = Read-Host "User Name"
	$password = Read-Host -AsSecureString 'Password'
	$outfilepath = $siteurl -replace ':', '_' -replace '/', '_'
	try
	{
	[Microsoft.SharePoint.Client.ClientContext]$cc = New-Object Microsoft.SharePoint.Client.ClientContext($siteurl)
	[Microsoft.SharePoint.Client.SharePointOnlineCredentials]$spocreds = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($username, $password)
	$cc.Credentials = $spocreds
	$site = $cc.Site;
	$sideLoadingGuid = new-object System.Guid "AE3A1339-61F5-4f8f-81A7-ABD2DA956A7D"
	$site.Features.Add($sideLoadingGuid, $true, [Microsoft.SharePoint.Client.FeatureDefinitionScope]::None);
	$cc.ExecuteQuery();
	Write-Host -ForegroundColor Green 'SideLoading feature enabled on site' $siteurl
	#Activate the Developer Site feature
	}
	catch
	{
	Write-Host -ForegroundColor Red 'Error encountered when trying to enable SideLoading feature' $siteurl, ':' $Error[0].ToString();
	}
	#CODE ENDS HERE

view raw gistfile1.ps1 hosted with ❤ by GitHub

It will ask SPO Site url. Enter SPO url.
It will ask SPO Administrator User name and password. Enter user name and password.

You will see:
SideLoadinf feature enabled on the site.....

That's it. Now deploy your app in to SharePoint Online.