Send email confirmation when BTC payment is confirmed

app/jobs/btcpay_check_donation_job.rb

@@ -4,15 +4,19 @@ class BtcpayCheckDonationJob < ApplicationJob
   def perform(donation)
     return if donation.completed?
 
-    invoice = BtcpayManager::FetchInvoice.call(invoice_id: donation.btcpay_invoice_id)
+    invoice = BtcpayManager::FetchInvoice.call(
+      invoice_id: donation.btcpay_invoice_id
+    )
 
     case invoice["status"]
     when "Settled"
-      # TODO use time from actual payment confirmation
       donation.paid_at = DateTime.now
       donation.payment_status = "settled"
       donation.save!
-      # TODO send email
+
+      NotificationMailer.with(user: donation.user)
+                        .bitcoin_donation_confirmed
+                        .deliver_later
     when "Processing"
       re_enqueue_job(donation)
     end