Add UMAD-11 for request

umad-11-request.md

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+# UMAD-11 Request
+
+UMA request is a way to deliver UMA invoices to sending wallets. Such as deep/universal links on 
+mobile, notification, etc.
+
+## Request for non-specified sender
+
+To deliver a UMA invoice to a sending wallet, the receiver can create a UMA invoice, and then
+deliver the encoded UMA invoice string to the sending wallet.
+
+The invoice string should be delivered using the following URL pattern:
+
+```raw
+uma://<invoice_string>
+```
+
+This can be displayed as a QR code, or a deep link on mobile. The sending wallet should register
+the `uma` scheme to handle the UMA invoice string.
+
+## Request for specified sender
+
+To deliver a UMA invoice with a specified sender, the receiver can create a UMA invoice, and then
+directly send the UMA invoice to the sending VASP.
+
+The request URL should be defined in the uma-configuration scheme (See UMAD-10 for details) as:
+
+```raw
+"uma_request_endpoint": "https://vasp1.com/path/to/request/url"
+```
+
+The sending VASP should implement the request endpoint as a POST endpoint that accepts the UMA 
+invoice. The payload should be a JSON object with the following fields:
+
+```raw
+{
+  "invoice": "<UMA invoice string>"
+}
+```
+
+Once sending VASP receives the UMA invoice, it should notify the sending wallet to confirm the payment.