diff --git a/supabase/functions/buildium-sync/index.ts b/supabase/functions/buildium-sync/index.ts
index 393fcd2..b7afce3 100644
--- a/supabase/functions/buildium-sync/index.ts
+++ b/supabase/functions/buildium-sync/index.ts
@@ -2123,12 +2123,21 @@ Deno.serve(async (req) => {
         const buildiumVendor = buildiumVendorById.get(String(bb.VendorId)) || null;
         const vendorId = await ensureVendor(buildiumVendor, assocLocalId);
 
-        // Pick first line's GL account as expense account if available
+        // Pick first line's GL account as expense account if available.
+        // chart_of_accounts.account_number stores the Buildium GL Id (see the
+        // glaccounts upsert: account_number = String(gl.Id ...)), so resolve the
+        // line's GL Id from whichever shape Buildium returns it in.
         const firstLine = Array.isArray(bb.Lines) && bb.Lines.length > 0 ? bb.Lines[0] : null;
         let expenseAccountId: string | null = null;
-        if (firstLine?.GLAccountId) {
+        const lineGlId = firstLine
+          ? (firstLine.GLAccountId
+            ?? firstLine.GLAccount?.Id
+            ?? firstLine.GLAccount?.GLAccountId
+            ?? null)
+          : null;
+        if (lineGlId !== null && lineGlId !== undefined && String(lineGlId) !== "") {
           const coa = await getCoa(assocLocalId);
-          expenseAccountId = coa.get(String(firstLine.GLAccountId)) || null;
+          expenseAccountId = coa.get(String(lineGlId)) || null;
         }
 
         let amount = Number(bb.TotalAmount ?? bb.Amount ?? 0);