Hi @Aniket Nade ,
For new SharePoint subscription Grant App Permission is disabled by default or the browser link https://xxxx-admin.sharepoint.com/_layouts/15/appinv.aspx is disabled. To enable this feature, we need to connect to SharePoint using Windows PowerShell and then run set-spotenant -DisableCustomAppAuthentication $false
.
Install-Module -Name Microsoft.Online.SharePoint.PowerShell
$adminUPN="<the full email address of a SharePoint administrator account, example: jdoe@contosotoycompany.onmicrosoft.com>"
$orgName="<name of your Office 365 organization, example: contosotoycompany>"
$userCredential = Get-Credential -UserName $adminUPN -Message "Type the password."
Connect-SPOService -Url https://$orgName-admin.sharepoint.com -Credential $userCredential
set-spotenant -DisableCustomAppAuthentication $false
Afterward, run https://<<domain>>/sites/<<site name>>/_layouts/15/appinv.aspx to grant permission
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