diff --git a/apps/api/src/__tests__/seed-uat-credentials.test.ts b/apps/api/src/__tests__/seed-uat-credentials.test.ts
index e04b7a9..aa1fdc0 100644
--- a/apps/api/src/__tests__/seed-uat-credentials.test.ts
+++ b/apps/api/src/__tests__/seed-uat-credentials.test.ts
@@ -32,12 +32,11 @@ const UAT_ACCOUNTS = [
 
 const TEST_PASSWORD = "test-password-123";
 
-// ─── Password hashing (must match the implementation in seed.ts) ───────────────
+// ─── Password hashing — must match better-auth/crypto (N=16384, r=16, p=1, dkLen=64, hex) ───
 
-function hashPassword(password: string): string {
-  const salt = randomBytes(16);
-  const hashed = scryptSync(password, salt, 64, { N: 4096, r: 8, p: 1 }).toString("base64");
-  return `${salt.toString("base64")}:${hashed}`;
+async function hashPassword(password: string): Promise<string> {
+  const { hashPassword } = await import("better-auth/crypto");
+  return hashPassword(password);
 }
 
 // ─── Mock DB state ─────────────────────────────────────────────────────────────
@@ -177,9 +176,9 @@ async function seedUatCredentials(
     if (existingAccount) {
       // skip — already has credential account
     } else {
-      const salt = randomBytes(16);
-      const hashed = scryptSync(password, salt, 64, { N: 4096, r: 8, p: 1 }).toString("base64");
-      const passwordHash = `${salt.toString("base64")}:${hashed}`;
+      // Use Better-Auth's hashPassword so test helper matches production seed.ts
+      const { hashPassword } = await import("better-auth/crypto");
+      const passwordHash = await hashPassword(password);
 
       const newAccount: AccountRow = {
         id: mockUuid(),
@@ -236,11 +235,12 @@ describe("seedUatCredentials — credential provisioning logic", () => {
     expect(insertedAccounts).toHaveLength(4);
     for (const acct of insertedAccounts) {
       expect(acct.providerId).toBe("credential");
-      expect(acct.password).toMatch(/^[A-Za-z0-9+/=]+:[A-Za-z0-9+/=]+$/); // salt:hash
-      // Verify the hash is scrypt with correct params
-      const [saltB64, hashB64] = acct.password!.split(":");
-      const salt = Buffer.from(saltB64, "base64");
-      const storedHash = Buffer.from(hashB64, "base64");
+      // Better-Auth uses hex encoding: saltHex:keyHex (both lowercase hex)
+      expect(acct.password).toMatch(/^[a-f0-9]+:[a-f0-9]+$/);
+      // Verify the hash is scrypt with correct params (N=16384, r=16, p=1, dkLen=64)
+      const [saltHex, keyHex] = acct.password!.split(":");
+      const salt = Buffer.from(saltHex, "hex");
+      const storedHash = Buffer.from(keyHex, "hex");
       expect(salt).toHaveLength(16);
       expect(storedHash).toHaveLength(64);
     }
@@ -271,13 +271,18 @@ describe("seedUatCredentials — credential provisioning logic", () => {
 
     const acct = insertedAccounts[0]!;
     expect(acct.providerId).toBe("credential");
-    const [saltB64, hashB64] = acct.password!.split(":");
-    expect(() => Buffer.from(saltB64, "base64")).not.toThrow();
-    expect(() => Buffer.from(hashB64, "base64")).not.toThrow();
-    // Verify the hash can be verified with the original password
-    const salt = Buffer.from(saltB64, "base64");
-    const storedHash = Buffer.from(hashB64, "base64");
-    const computed = scryptSync(TEST_PASSWORD, salt, 64, { N: 4096, r: 8, p: 1 });
+    // Better-Auth uses hex: saltHex (32 chars) : keyHex (128 chars)
+    expect(acct.password).toMatch(/^[a-f0-9]+:[a-f0-9]+$/);
+    const [saltHex, keyHex] = acct.password!.split(":");
+    expect(() => Buffer.from(saltHex, "hex")).not.toThrow();
+    expect(() => Buffer.from(keyHex, "hex")).not.toThrow();
+    const salt = Buffer.from(saltHex, "hex");
+    const storedHash = Buffer.from(keyHex, "hex");
+    expect(salt).toHaveLength(16);
+    expect(storedHash).toHaveLength(64);
+    // Verify the hash can be verified with the original password using Better-Auth params
+    const { scryptSync } = await import("node:crypto");
+    const computed = scryptSync(TEST_PASSWORD.normalize("NFKC"), saltHex, 64, { N: 16384, r: 16, p: 1 });
     expect(computed).toEqual(storedHash);
   });
 
diff --git a/apps/api/src/db/seed.ts b/apps/api/src/db/seed.ts
index a12699a..566da17 100644
--- a/apps/api/src/db/seed.ts
+++ b/apps/api/src/db/seed.ts
@@ -563,13 +563,11 @@ async function seedKnownUsers() {
     if (existingAccount) {
       console.log(`✓ Credential account for '${acct.email}' already exists — skipping`);
     } else {
-      // Hash password using the same scrypt derivation as crypto.ts (AES-256-GCM key derivation).
-      // Better-Auth defaults to scrypt for password hashing; match those parameters here.
-      const { scryptSync, randomBytes } = await import("node:crypto");
-      const salt = randomBytes(16);
-      // scryptSync(password, salt, keylen=64, N=32768, r=8, p=1) — matches common better-auth scrypt params
-      const hashed = scryptSync(password, salt, 64, { N: 32768, r: 8, p: 1 }).toString("base64");
-      const passwordHash = `${salt.toString("base64")}:${hashed}`;
+      // Use Better-Auth's own hashPassword to guarantee parameter/encoding match.
+      // better-auth/crypto uses: N=16384, r=16, p=1, dkLen=64, salt as 16-byte random
+      // hex string, key hex-encoded, format saltHex:keyHex.
+      const { hashPassword } = await import("better-auth/crypto");
+      const passwordHash = await hashPassword(password);
 
       await db.insert(schema.account).values({
         id: uuid(),