diff --git a/ai-transpiler-demo.ipynb b/ai-transpiler-demo.ipynb
index d4c0c42..8f1cf23 100644
--- a/ai-transpiler-demo.ipynb
+++ b/ai-transpiler-demo.ipynb
@@ -212,7 +212,7 @@
     "\n",
     "qiskit_lvl3_transpiler_service = TranspilerService(\n",
     "    backend_name=\"ibm_torino\",\n",
-    "    ai='false',\n",
+    "    ai=\"false\",\n",
     "    optimization_level=3,\n",
     ")"
    ]
@@ -281,7 +281,7 @@
    "source": [
     "qiskit_lvl3_ai_transpiler_service = TranspilerService(\n",
     "    backend_name=\"ibm_torino\",\n",
-    "    ai='true',\n",
+    "    ai=\"true\",\n",
     "    optimization_level=3,\n",
     ")"
    ]
diff --git a/documentation-examples.ipynb b/documentation-examples.ipynb
index 494179d..6d9bfca 100644
--- a/documentation-examples.ipynb
+++ b/documentation-examples.ipynb
@@ -22,7 +22,7 @@
     "\n",
     "cloud_transpiler_service = TranspilerService(\n",
     "    backend_name=\"ibm_sherbrooke\",\n",
-    "    ai='false',\n",
+    "    ai=\"false\",\n",
     "    optimization_level=3,\n",
     ")\n",
     "transpiled_circuit_no_ai = cloud_transpiler_service.run(circuit)"
@@ -50,7 +50,7 @@
     "\n",
     "cloud_transpiler_service = TranspilerService(\n",
     "    backend_name=\"ibm_sherbrooke\",\n",
-    "    ai='true',\n",
+    "    ai=\"true\",\n",
     "    optimization_level=1,\n",
     ")\n",
     "transpiled_circuit_ai = cloud_transpiler_service.run(circuit)"
diff --git a/qiskit_transpiler_service/transpiler_service.py b/qiskit_transpiler_service/transpiler_service.py
index 9741123..6b6ee6c 100644
--- a/qiskit_transpiler_service/transpiler_service.py
+++ b/qiskit_transpiler_service/transpiler_service.py
@@ -57,7 +57,7 @@ class TranspilerService:
     def __init__(
         self,
         optimization_level: int,
-        ai: Literal['true', 'false', 'auto'] = 'true',
+        ai: Literal["true", "false", "auto"] = "true",
         coupling_map: Union[List[List[int]], None] = None,
         backend_name: Union[str, None] = None,
         qiskit_transpile_options: Dict = None,
diff --git a/qiskit_transpiler_service/wrappers/base.py b/qiskit_transpiler_service/wrappers/base.py
index e7afdb9..0b68ddc 100644
--- a/qiskit_transpiler_service/wrappers/base.py
+++ b/qiskit_transpiler_service/wrappers/base.py
@@ -129,9 +129,9 @@ def request_and_wait(self, endpoint: str, body: Dict, params: Dict):
             return self._request_and_wait(endpoint, body, params)
         except requests.exceptions.HTTPError as exc:
             _raise_transpiler_error_and_log(_get_error_msg_from_response(exc))
-        except BackendTaskError:
-            # TODO: Do we want to give the user the internal error: "The background task df86e449-8bb5-43fb-92a9-c23818ee8ce7 FAILED"
-            _raise_transpiler_error_and_log("Service error.")
+        except BackendTaskError as exc:
+            error_msg = exc.msg or "Service error."
+            _raise_transpiler_error_and_log(error_msg)
         except Exception as exc:
             _raise_transpiler_error_and_log(f"Error: {exc}")
 
@@ -173,18 +173,18 @@ def _raise_transpiler_error_and_log(msg: str):
 
 
 def _get_error_msg_from_response(exc: requests.exceptions.HTTPError):
-    if exc.response.status_code == HTTPStatus.UNPROCESSABLE_ENTITY.value:
-        # Default message
-        msg = "Internal error."
-        resp = exc.response.json()
-        if detail := resp.get("detail"):
-            if isinstance(detail, str):
-                msg = detail
-            elif isinstance(detail, list):
-                # Try to get err msg from
-                # raw validation error
-                if "input" in resp["detail"][0] and "msg" in resp["detail"][0]:
-                    msg = f"Wrong input '{resp['detail'][0]['input']}'. {resp['detail'][0]['msg']}"
-    else:
-        msg = f"Service error: {str(exc)}"
+    resp = exc.response.json()
+    detail = resp.get("detail")
+    # Default message
+    msg = "Internal error."
+
+    if isinstance(detail, str):
+        msg = detail
+    elif isinstance(detail, list):
+        detail_input = detail[0]["input"]
+        detail_msg = detail[0]["msg"]
+
+        if detail_input and detail_msg:
+            msg = f"Wrong input '{detail_input}'. {detail_msg}"
+
     return msg
diff --git a/qiskit_transpiler_service/wrappers/transpile.py b/qiskit_transpiler_service/wrappers/transpile.py
index 053b126..96f02ef 100644
--- a/qiskit_transpiler_service/wrappers/transpile.py
+++ b/qiskit_transpiler_service/wrappers/transpile.py
@@ -43,7 +43,7 @@ def transpile(
         optimization_level: int = 1,
         backend: Union[str, None] = None,
         coupling_map: Union[List[List[int]], None] = None,
-        ai: Literal['true', 'false', 'auto'] = 'true',
+        ai: Literal["true", "false", "auto"] = "true",
         qiskit_transpile_options: Dict = None,
         ai_layout_mode: str = None,
     ):
diff --git a/tests/test_transpiler_service.py b/tests/test_transpiler_service.py
index 4661ab0..b6ba796 100644
--- a/tests/test_transpiler_service.py
+++ b/tests/test_transpiler_service.py
@@ -32,7 +32,7 @@
 @pytest.mark.parametrize(
     "optimization_level", [1, 2, 3], ids=["opt_level_1", "opt_level_2", "opt_level_3"]
 )
-@pytest.mark.parametrize("ai", ['false', 'true'], ids=["no_ai", "ai"])
+@pytest.mark.parametrize("ai", ["false", "true"], ids=["no_ai", "ai"])
 @pytest.mark.parametrize(
     "qiskit_transpile_options",
     [None, {"seed_transpiler": 0}],
@@ -56,7 +56,7 @@ def test_rand_circ_backend_routing(optimization_level, ai, qiskit_transpile_opti
 @pytest.mark.parametrize(
     "optimization_level", [1, 2, 3], ids=["opt_level_1", "opt_level_2", "opt_level_3"]
 )
-@pytest.mark.parametrize("ai", ['false', 'true'], ids=["no_ai", "ai"])
+@pytest.mark.parametrize("ai", ["false", "true"], ids=["no_ai", "ai"])
 @pytest.mark.parametrize(
     "qiskit_transpile_options",
     [None, {"seed_transpiler": 0}],
@@ -85,7 +85,7 @@ def test_qv_backend_routing(optimization_level, ai, qiskit_transpile_options):
     ],
 )
 @pytest.mark.parametrize("optimization_level", [1, 2, 3])
-@pytest.mark.parametrize("ai", ['false', 'true'], ids=["no_ai", "ai"])
+@pytest.mark.parametrize("ai", ["false", "true"], ids=["no_ai", "ai"])
 @pytest.mark.parametrize("qiskit_transpile_options", [None, {"seed_transpiler": 0}])
 def test_rand_circ_cmap_routing(
     coupling_map, optimization_level, ai, qiskit_transpile_options
@@ -108,7 +108,7 @@ def test_qv_circ_several_circuits_routing():
 
     cloud_transpiler_service = TranspilerService(
         backend_name="ibm_brisbane",
-        ai='true',
+        ai="true",
         optimization_level=1,
     )
     transpiled_circuit = cloud_transpiler_service.run([qv_circ] * 2)
@@ -129,7 +129,7 @@ def test_qv_circ_wrong_input_routing():
 
     cloud_transpiler_service = TranspilerService(
         backend_name="ibm_brisbane",
-        ai='true',
+        ai="true",
         optimization_level=1,
     )
 
@@ -138,7 +138,7 @@ def test_qv_circ_wrong_input_routing():
         cloud_transpiler_service.run(circ_dict)
 
 
-@pytest.mark.parametrize("ai", ['false', 'true'], ids=["no_ai", "ai"])
+@pytest.mark.parametrize("ai", ["false", "true"], ids=["no_ai", "ai"])
 def test_transpile_layout_reconstruction(ai):
     n_qubits = 27
 
@@ -161,6 +161,81 @@ def test_transpile_layout_reconstruction(ai):
         )
 
 
+def test_transpile_non_valid_backend():
+    circuit = EfficientSU2(100, entanglement="circular", reps=1).decompose()
+    non_valid_backend_name = "ibm_torin"
+    transpiler_service = TranspilerService(
+        backend_name=non_valid_backend_name,
+        ai="false",
+        optimization_level=3,
+    )
+
+    try:
+        transpiler_service.run(circuit)
+        pytest.fail("Error expected")
+    except Exception as e:
+        assert (
+            str(e)
+            == f'"User doesn\'t have access to the specified backend: {non_valid_backend_name}"'
+        )
+
+
+def test_transpile_exceed_circuit_size():
+    circuit = EfficientSU2(100, entanglement="circular", reps=50).decompose()
+    transpiler_service = TranspilerService(
+        backend_name="ibm_kyoto",
+        ai="false",
+        optimization_level=3,
+    )
+
+    try:
+        transpiler_service.run(circuit)
+        pytest.fail("Error expected")
+    except Exception as e:
+        assert str(e) == "'Circuit has more gates than the allowed maximum of 5000.'"
+
+
+def test_transpile_malformed_body():
+    circuit = EfficientSU2(100, entanglement="circular", reps=1).decompose()
+    transpiler_service = TranspilerService(
+        backend_name="ibm_kyoto",
+        ai="false",
+        optimization_level=3,
+        qiskit_transpile_options={"failing_option": 0},
+    )
+
+    try:
+        transpiler_service.run(circuit)
+        pytest.fail("Error expected")
+    except Exception as e:
+        assert (
+            str(e)
+            == "\"transpile() got an unexpected keyword argument 'failing_option'\""
+        )
+
+
+def test_transpile_failing_task():
+    open_qasm_circuit = 'OPENQASM 2.0;\ninclude "qelib1.inc";\ngate dcx q0,q1 { cx q0,q1; cx q1,q0; }\nqreg q[3];\ncz q[0],q[2];\nsdg q[1];\ndcx q[2],q[1];\nu3(3.890139082217223,3.447697582994976,1.1583481971959322) q[0];\ncrx(2.3585459177723522) q[1],q[0];\ny q[2];'
+    circuit = QuantumCircuit.from_qasm_str(open_qasm_circuit)
+    transpiler_service = TranspilerService(
+        backend_name="ibm_kyoto",
+        ai="false",
+        optimization_level=3,
+        coupling_map=[[1, 2], [2, 1]],
+        qiskit_transpile_options={
+            "basis_gates": ["u1", "u2", "u3", "cx"],
+            "seed_transpiler": 0,
+        },
+    )
+
+    try:
+        transpiler_service.run(circuit)
+        pytest.fail("Error expected")
+    except Exception as e:
+        assert "The background task" in str(e)
+        assert "FAILED" in str(e)
+
+
 def compare_layouts(plugin_circ, non_ai_circ):
     assert (
         plugin_circ.layout.initial_layout == non_ai_circ.layout.initial_layout