sign_tx: return the error message when additional_info parsing fails

diff --git a/main/process/sign_psbt.c b/main/process/sign_psbt.c
index 3fb6d94..140a709 100644
--- a/main/process/sign_psbt.c
+++ b/main/process/sign_psbt.c
@@ -693,8 +693,8 @@ int sign_psbt(jade_process_t* process, CborValue* params, const network_t networ
     // Liquid: Get any data from the optional 'additional_info' section
     if (for_liquid && process && params
         && !params_additional_info(
-            process, params, tx, &txtype, &is_partial, &in_sums, &num_in_sums, &out_sums, &num_out_sums)) {
-        // Note in_sums/out_sums are cleared automatically at proces exit
+            process, params, tx, &txtype, &is_partial, &in_sums, &num_in_sums, &out_sums, &num_out_sums, errmsg)) {
+        // Note in_sums/out_sums are cleared automatically at process exit
         retval = CBOR_RPC_BAD_PARAMETERS;
         goto cleanup_tx;
     }
diff --git a/main/process/sign_tx.c b/main/process/sign_tx.c
index 487b9a5..87fe2da 100644
--- a/main/process/sign_tx.c
+++ b/main/process/sign_tx.c
@@ -464,6 +464,7 @@ static void sign_tx_impl(jade_process_t* process, const bool for_liquid)
         JADE_LOGI("Read %d assets from message", num_assets);
     }
 
+    const char* errmsg = NULL;
     asset_summary_t *in_sums = NULL, *out_sums = NULL;
     size_t num_in_sums = 0, num_out_sums = 0;
     bool is_partial = false;
@@ -471,14 +472,14 @@ static void sign_tx_impl(jade_process_t* process, const bool for_liquid)
     // Liquid: Get any data from the optional 'additional_info' section
     if (for_liquid
         && !params_additional_info(
-            process, &params, tx, &txtype, &is_partial, &in_sums, &num_in_sums, &out_sums, &num_out_sums)) {
+            process, &params, tx, &txtype, &is_partial, &in_sums, &num_in_sums, &out_sums, &num_out_sums, &errmsg)) {
+        jade_process_reject_message(process, CBOR_RPC_BAD_PARAMETERS, errmsg);
         goto cleanup;
     }
 
     // Liquid: Gather the (unblinded) output info for user confirmation,
     // then validate output and additional_info values
     if (for_liquid) {
-        const char* errmsg = NULL;
         if (!update_elements_outputs(tx, commitments, output_info, &errmsg)
             || !validate_elements_outputs(
                 network_id, tx, txtype, output_info, in_sums, num_in_sums, out_sums, num_out_sums, &errmsg)) {
@@ -569,7 +570,6 @@ static void sign_tx_impl(jade_process_t* process, const bool for_liquid)
         // (But if passed must be valid - empty/root path is not allowed for signing)
         const bool has_path = rpc_has_field_data("path", &params);
         if (has_path) {
-            const char* errmsg = NULL;
             num_to_sign += 1;
 
             // Get all common tx-signing input fields which must be present if a path is given
diff --git a/main/process/sign_utils.c b/main/process/sign_utils.c
index 5f0074c..7de2dd0 100644
--- a/main/process/sign_utils.c
+++ b/main/process/sign_utils.c
@@ -155,21 +155,21 @@ static void rpc_get_asset_summary(
     }
 }
 
-static bool validate_additional_info(jade_process_t* process, const struct wally_tx* tx, const TxType_t txtype,
-    const bool is_partial, const asset_summary_t* in_sums, const size_t num_in_sums, const asset_summary_t* out_sums,
-    const size_t num_out_sums)
+static bool validate_additional_info(const struct wally_tx* tx, const TxType_t txtype, const bool is_partial,
+    const asset_summary_t* in_sums, const size_t num_in_sums, const asset_summary_t* out_sums,
+    const size_t num_out_sums, const char** errmsg)
 {
-    const char* errmsg = NULL;
     // Shouldn't have pointers to empty arrays
     JADE_ASSERT(!in_sums == !num_in_sums);
     JADE_ASSERT(!out_sums == !num_out_sums);
+    JADE_INIT_OUT_PPTR(errmsg);
 
     // Validate tx type data
     if (txtype == TXTYPE_SWAP) {
         // Input and output summary must be present - they will be fully validated later
         if (!in_sums || !out_sums) {
-            errmsg = "Swap tx missing input/output summary information";
-            goto done;
+            *errmsg = "Swap tx missing input/output summary information";
+            return false;
         }
 
         // Validate swap or proposal appears to have expected inputs and outputs
@@ -178,30 +178,26 @@ static bool validate_additional_info(jade_process_t* process, const struct wally
             // input and exactly one output which is to self, and in a different asset to the input
             if (tx->num_inputs != 1 || tx->num_outputs != 1 || num_in_sums != 1 || num_out_sums != 1
                 || !memcmp(in_sums[0].asset_id, out_sums[0].asset_id, sizeof(out_sums[0].asset_id))) {
-                errmsg = "Initial swap proposal must have single wallet input and output in different assets";
-                goto done;
+                *errmsg = "Initial swap proposal must have single wallet input and output in different assets";
+                return false;
             }
         } else {
             // TODO: Ideally check total number of assets in our inputs and outputs
             if (tx->num_inputs < 2 || tx->num_outputs < 2) {
-                errmsg = "Insufficient inputs/outputs for a swap tx";
-                goto done;
+                *errmsg = "Insufficient inputs/outputs for a swap tx";
+                return false;
             }
         }
     } else if (txtype != TXTYPE_SEND_PAYMENT) {
-        errmsg = "Unsupported tx-type in additional info";
-        goto done;
-    }
-done:
-    if (errmsg) {
-        jade_process_reject_message(process, CBOR_RPC_BAD_PARAMETERS, errmsg);
+        *errmsg = "Unsupported tx-type in additional info";
         return false;
     }
     return true;
 }
 
 TxType_t params_additional_info(jade_process_t* process, CborValue* params, const struct wally_tx* tx, TxType_t* txtype,
-    bool* is_partial, asset_summary_t** in_sums, size_t* num_in_sums, asset_summary_t** out_sums, size_t* num_out_sums)
+    bool* is_partial, asset_summary_t** in_sums, size_t* num_in_sums, asset_summary_t** out_sums, size_t* num_out_sums,
+    const char** errmsg)
 {
     JADE_ASSERT(params);
     JADE_ASSERT(tx);
@@ -211,6 +207,7 @@ TxType_t params_additional_info(jade_process_t* process, CborValue* params, cons
     JADE_INIT_OUT_SIZE(num_in_sums);
     JADE_INIT_OUT_PPTR(out_sums);
     JADE_INIT_OUT_SIZE(num_out_sums);
+    JADE_INIT_OUT_PPTR(errmsg);
 
     *is_partial = false;
     *txtype = TXTYPE_SEND_PAYMENT;
@@ -230,10 +227,10 @@ TxType_t params_additional_info(jade_process_t* process, CborValue* params, cons
 
     // Tx Type
     if (!rpc_get_txtype(process, &additional_info, txtype)) {
+        *errmsg = "Failed to extract tx type from additional_info";
         return false;
     }
-    if (!validate_additional_info(
-            process, tx, *txtype, *is_partial, *in_sums, *num_in_sums, *out_sums, *num_out_sums)) {
+    if (!validate_additional_info(tx, *txtype, *is_partial, *in_sums, *num_in_sums, *out_sums, *num_out_sums, errmsg)) {
         return false;
     }
     return true;
diff --git a/main/process/sign_utils.h b/main/process/sign_utils.h
index 83a9eb7..aa021a3 100644
--- a/main/process/sign_utils.h
+++ b/main/process/sign_utils.h
@@ -26,7 +26,8 @@ bool params_trusted_commitments(
     jade_process_t* process, const CborValue* params, const struct wally_tx* tx, commitment_t** data);
 
 TxType_t params_additional_info(jade_process_t* process, CborValue* params, const struct wally_tx* tx, TxType_t* txtype,
-    bool* is_partial, asset_summary_t** in_sums, size_t* num_in_sums, asset_summary_t** out_sums, size_t* num_out_sums);
+    bool* is_partial, asset_summary_t** in_sums, size_t* num_in_sums, asset_summary_t** out_sums, size_t* num_out_sums,
+    const char** errmsg);
 
 // Returns true if commitments are present and validated correctly.
 // Returns false otherwise, with errmsg set if an error occurred, or