CSV headers: InvitedUserEmailAddress, DispName, RedirectURL

AzureAD - Invite guest users.ps1

# connect 
$cred = Get-Credential
Connect-AzureAD -Credential $cred

# setting variables
$invitations = import-csv ..\invitations.csv
$messageInfo = New-Object Microsoft.Open.MSGraph.Model.InvitedUserMessageInfo
$messageInfo.customizedMessageBody = "Hey there! Check this out. I created an invitation through PowerShell"

# loop
foreach ($email in $invitations) {
New-AzureADMSInvitation -InvitedUserEmailAddress $email.InvitedUserEmailAddress -InvitedUserDisplayName $email.DispName -InviteRedirectUrl $email.RedirectURL -InvitedUserMessageInfo $messageInfo -SendInvitationMessage $true
}