diff --git a/fava_client.py b/fava_client.py
index 3c9861d..ab8c57a 100644
--- a/fava_client.py
+++ b/fava_client.py
@@ -652,7 +652,7 @@ class FavaClient:
             async with httpx.AsyncClient(timeout=self.timeout) as client:
                 response = await client.delete(
                     f"{self.base_url}/source_slice",
-                    json={
+                    params={
                         "entry_hash": entry_hash,
                         "sha256sum": sha256sum
                     }
diff --git a/views_api.py b/views_api.py
index bf72ee8..a5f54ca 100644
--- a/views_api.py
+++ b/views_api.py
@@ -2017,7 +2017,10 @@ async def api_reject_expense_entry(
     wallet: WalletTypeInfo = Depends(require_admin_key),
 ) -> dict:
     """
-    Reject a pending expense entry by deleting it from the Beancount file (admin only).
+    Reject a pending expense entry by marking it as voided (admin only).
+
+    Adds #voided tag for audit trail while keeping the '!' flag.
+    Voided transactions are excluded from balances but preserved in the ledger.
     """
     from lnbits.settings import settings as lnbits_settings
     from .fava_client import get_fava_client
@@ -2058,18 +2061,47 @@ async def api_reject_expense_entry(
             detail=f"Pending entry {entry_id} not found in Beancount ledger"
         )
 
-    # 3. Get the entry context for sha256sum
+    # 3. Get the entry context (source text + sha256sum)
     context = await fava.get_entry_context(target_entry_hash)
+    source = context.get("slice", "")
     sha256sum = context.get("sha256sum", "")
 
-    # 4. Delete the entry
-    result = await fava.delete_entry(target_entry_hash, sha256sum)
+    if not source:
+        raise HTTPException(
+            status_code=HTTPStatus.INTERNAL_SERVER_ERROR,
+            detail="Could not retrieve entry source from Fava"
+        )
+
+    # 4. Add #voided tag (keep ! flag as per convention)
+    date_str = target_entry.get("date", "")
+
+    # Add #voided tag if not already present
+    if "#voided" not in source:
+        # Find the transaction line and add #voided to the tags
+        # Pattern: date ! "narration" #existing-tags
+        lines = source.split('\n')
+        for i, line in enumerate(lines):
+            if date_str in line and '"' in line and '!' in line:
+                # Add #voided tag to the transaction line
+                if '#' in line:
+                    # Already has tags, append voided
+                    lines[i] = line.rstrip() + ' #voided'
+                else:
+                    # No tags yet, add after narration
+                    lines[i] = line.rstrip() + ' #voided'
+                break
+        new_source = '\n'.join(lines)
+    else:
+        new_source = source
+
+    # 5. Update the entry via Fava API
+    await fava.update_entry_source(target_entry_hash, new_source, sha256sum)
 
     return {
-        "message": f"Entry {entry_id} rejected and deleted successfully",
+        "message": f"Entry {entry_id} rejected (marked as voided)",
         "entry_id": entry_id,
         "entry_hash": target_entry_hash,
-        "date": target_entry.get("date", ""),
+        "date": date_str,
         "description": target_entry.get("narration", "")
     }