test: reproduce WIRE_INVALID_ONION_PAYLOAD

```
>           raise RpcError(method, payload, resp['error'])
E           pyln.client.lightning.RpcError: RPC call failed: method: pay, payload: {'bolt11': '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'}, error: {'code': 203, 'message': 'failed: WIRE_INVALID_ONION_PAYLOAD (reply from remote)', 'id': 1, 'failcode': 16406, 'failcodename': 'WIRE_INVALID_ONION_PAYLOAD', 'bolt12': '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', 'raw_message': '40160a0068', 'created_at': 1724699621, 'destination': '032cf15d1ad9c4a08d26eab1918f732d8ef8fdc6abb9640bf3db174372c491304e', 'payment_hash': 'e170c7d38854867db0c11e78b760b573307192be67f7a961cd4010533e281efd', 'status': 'failed', 'amount_msat': 3, 'amount_sent_msat': 0, 'erring_index': 2, 'erring_node': '035d2b1192dfba134e10e540875d366ebc8bc353d5aa766b80c090b39c3a5d885d'}

contrib/pyln-client/pyln/client/lightning.py:416: RpcError
```

Signed-off-by: Vincenzo Palazzo <[email protected]>

tests/test_pay.py

@@ -5996,3 +5996,47 @@ def test_enableoffer(node_factory):
     # Can't enable unknown.
     with pytest.raises(RpcError, match="Unknown offer"):
         l1.rpc.enableoffer(offer_id=offer1['offer_id'])
+
+
+def test_offer_with_private_channels(node_factory):
+    """We should be able to fetch an invoice through a private path"""
+    l1, l2, l3 = node_factory.line_graph(3, fundchannel=False, opts={'experimental-offers': None})
+
+    # Private channel from l2->l3, makes l3 add a blinded path to invoice
+    # (l1's existence makes sure l3 doesn't see l2 as a dead end!)
+    node_factory.join_nodes([l1, l2], wait_for_announce=True)
+    node_factory.join_nodes([l2, l3], announce_channels=False)
+    wait_for(lambda: ['alias' in n for n in l3.rpc.listnodes()['nodes']] == [True, True])
+
+    offer = l3.rpc.offer(amount='2msat', description='test_offer_path_self')['bolt12']
+    invoice = l1.rpc.fetchinvoice(offer=offer)["invoice"]
+    assert l1.rpc.pay(invoice) is not None
+
+
+def test_offer_with_private_channels_multyhop(node_factory):
+    """We should be able to fetch an invoice through a private path and pay the invoice"""
+    l1, l2, l3, l4 = node_factory.line_graph(4, fundchannel=False, opts={'experimental-offers': None})
+
+    node_factory.join_nodes([l1, l2], wait_for_announce=True)
+    node_factory.join_nodes([l2, l3], wait_for_announce=True)
+    node_factory.join_nodes([l3, l4], announce_channels=False)
+    wait_for(lambda: ['alias' in n for n in l4.rpc.listnodes()['nodes']] == [True, True, True])
+
+    offer = l4.rpc.offer(amount='2msat', description='test_offer_with_private_channels_multyhop')['bolt12']
+    invoice = l1.rpc.fetchinvoice(offer=offer)["invoice"]
+    assert l1.rpc.pay(invoice) is not None
+
+
+def test_offer_with_private_channels_multyhop2(node_factory):
+    """We should be able to fetch an invoice through a private path and pay the invoice"""
+    l1, l2, l3, l4, l5 = node_factory.line_graph(5, fundchannel=False, opts={'experimental-offers': None})
+
+    node_factory.join_nodes([l1, l2], wait_for_announce=True)
+    node_factory.join_nodes([l2, l3], wait_for_announce=True)
+    node_factory.join_nodes([l3, l4], wait_for_announce=True)
+    node_factory.join_nodes([l3, l5], announce_channels=False)
+    wait_for(lambda: ['alias' in n for n in l4.rpc.listnodes()['nodes']] == [True, True, True, True])
+
+    offer = l5.rpc.offer(amount='2msat', description='test_offer_with_private_channels_multyhop2')['bolt12']
+    invoice = l1.rpc.fetchinvoice(offer=offer)["invoice"]
+    assert l1.rpc.pay(invoice) is not None