diff --git a/src/avalanche/delegation.cpp b/src/avalanche/delegation.cpp
--- a/src/avalanche/delegation.cpp
+++ b/src/avalanche/delegation.cpp
@@ -76,7 +76,8 @@
 
     bool ret = reduceLevels(hash, levels, [&](const Level &l) {
         if (!pauth->VerifySchnorr(hash, l.sig)) {
-            return state.Invalid(DelegationResult::INVALID_SIGNATURE);
+            return state.Invalid(DelegationResult::INVALID_SIGNATURE,
+                                 "invalid-signature");
         }
 
         // This key is valid, now up to the next delegation level.
diff --git a/src/rpc/avalanche.cpp b/src/rpc/avalanche.cpp
--- a/src/rpc/avalanche.cpp
+++ b/src/rpc/avalanche.cpp
@@ -384,22 +384,21 @@
 
         if (dg.getProofId() !=
             limitedProofId.computeProofId(dg.getProofMaster())) {
-            throw JSONRPCError(
-                RPC_INVALID_PARAMETER,
-                "The supplied delegation does not match the proof");
+            throw JSONRPCError(RPC_INVALID_PARAMETER,
+                               "The delegation does not match the proof");
         }
 
         CPubKey auth;
         avalanche::DelegationState dgState;
         if (!dg.verify(dgState, auth)) {
             throw JSONRPCError(RPC_INVALID_PARAMETER,
-                               "The supplied delegation is not valid");
+                               "The delegation is invalid: " +
+                                   dgState.ToString());
         }
 
         if (privkey.GetPubKey() != auth) {
-            throw JSONRPCError(
-                RPC_INVALID_PARAMETER,
-                "The supplied private key does not match the delegation");
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY,
+                               "The private key does not match the delegation");
         }
 
         dgb = std::make_unique<avalanche::DelegationBuilder>(dg);
diff --git a/test/functional/abc_rpc_avalancheproof.py b/test/functional/abc_rpc_avalancheproof.py
--- a/test/functional/abc_rpc_avalancheproof.py
+++ b/test/functional/abc_rpc_avalancheproof.py
@@ -201,7 +201,7 @@
 
         # Invalid delegation
         bad_dg = AvalancheDelegation()
-        assert_raises_rpc_error(-8, "The supplied delegation does not match the proof",
+        assert_raises_rpc_error(-8, "The delegation does not match the proof",
                                 node.delegateavalancheproof,
                                 limited_id_hex,
                                 bytes_to_wif(privkey.get_bytes()),
@@ -213,7 +213,7 @@
         bad_dg.limited_proofid = proofobj.limited_proofid
         bad_dg.proof_master = proofobj.master
         bad_dg.levels = [AvalancheDelegationLevel()]
-        assert_raises_rpc_error(-8, "The supplied delegation is not valid",
+        assert_raises_rpc_error(-8, "The delegation is invalid",
                                 node.delegateavalancheproof,
                                 limited_id_hex,
                                 bytes_to_wif(privkey.get_bytes()),
@@ -222,7 +222,7 @@
                                 )
 
         # Wrong privkey, match the proof but does not match the delegation
-        assert_raises_rpc_error(-8, "The supplied private key does not match the delegation",
+        assert_raises_rpc_error(-5, "The private key does not match the delegation",
                                 node.delegateavalancheproof,
                                 limited_id_hex,
                                 bytes_to_wif(privkey.get_bytes()),