Bagisto Marketplace: “The requested quantity is not available” on add-to-cart (seller flow) despite seller stock visible on channel

[Radoje]

Symptom

When adding a seller product to cart from PDP, we consistently get:
The requested quantity is not available, please try again later.
packages/Webkul/Marketplace/src/Cart.php:108
The same happens if we call add-to-cart from a small diagnostic route (Product object + seller context).

What we have verified

1. Product / stock / channel mapping

• product_flat (product_id=54) → price=60, status=1, visible_individually=1, weight=5.
• Seller stock exists (vendor_id = 2) and channel sees source #5:
  -- seller-scoped stock in active channel (returns 7)
  SELECT SUM(pi.qty) AS salable_qty_seller
  FROM product_inventories pi
  JOIN channel_inventory_sources cis ON cis.inventory_source_id = pi.inventory_source_id
  WHERE pi.product_id = 54
  AND pi.vendor_id = 2
  AND cis.channel_id = 1;
• Raw inventory row:
  SELECT * FROM product_inventories
  WHERE product_id=54 AND vendor_id=2;
  -- → (id=?, qty=7, product_id=54, vendor_id=2, inventory_source_id=5)
• Channel “Balkan” inventory sources = 1, 2, 5 (vendor source #5 enabled).
• Seller panel → Settings → Inventory Sources → source #5 Active.

2. Marketplace tables

• Marketplace product row exists & approved:
  SELECT * FROM marketplace_products WHERE product_id=54;
  /* → id=34, product_id=54, marketplace_seller_id=2, is_approved=1, is_owner=1 */

3. Seller payload we submit
   We post a complete seller context (product object, not ID):
   {
   "product_id": 54,
   "quantity": 1,
   "seller_id": 2,
   "marketplace_seller_id": 2,
   "seller_product_id": 34,
   "inventory_source_id": 5,
   "vendor_id": 2
   }

4. Route & middlewares
   We load a small proxy route under shop middlewares:
   // app/Providers/MpRouteServiceProvider.php
   Route::middleware(['web','channel','theme','locale','currency'])
   ->group(base_path('routes/mp.php'));

// routes/mp.php (excerpt)
Route::post('/mp-add-to-cart', function (Request $r, ProductRepository $products) {
$p = $products->findOrFail((int) $r->input('product_id')); // Product OBJECT

$data = $r->validate([
    'product_id'             => 'required|integer',
    'quantity'               => 'nullable|integer|min:1',
    'seller_id'              => 'nullable|integer',
    'seller_product_id'      => 'nullable|integer',
    'marketplace_seller_id'  => 'nullable|integer',
    'inventory_source_id'    => 'nullable|integer',
    'vendor_id'              => 'nullable|integer',
]);

$payload = ['quantity' => (int)($data['quantity'] ?? 1)];
foreach (['seller_id','seller_product_id','marketplace_seller_id','inventory_source_id','vendor_id'] as $k) {
    if (!empty($data[$k])) $payload[$k] = (int) $data[$k];
}

\Log::error('MP ADD payload', $payload); // we see it in logs

// Marketplace Cart first:
try {
    \Webkul\Checkout\Facades\Cart::addProduct($p, $payload);
} catch (\Throwable $e) {
    // TEMP fallback so checkout doesn’t block (works):
    if (str_contains($e->getMessage(), 'requested quantity')) {
        app(\Webkul\Checkout\Cart::class)->addProduct($p, ['quantity' => $payload['quantity']]);
    } else {
        throw $e;
    }
}
return redirect('/checkout/cart');

});

5. PDP seller CTA
   On PDP we render seller info and post to /mp-add-to-cart with the payload fields above.

The problem

Even with the complete seller payload (and channel seeing source #5), Marketplace Cart still throws “requested quantity is not available …” from Marketplace/src/Cart.php:108.
If we enable the core fallback in our route, item is added to cart and checkout works; but we’d like to keep the pure Marketplace flow.

Question

For this Bagisto Marketplace build, what exact parameter(s) or flag does Marketplace Cart need at addProduct($product, $data) to pick the seller stock in the active channel?

We already include: seller_product_id, marketplace_seller_id, vendor_id, inventory_source_id, and the route runs with web, channel, theme, locale, currency.

Seller stock (vendor_id=2 on source_id=5) is present and visible to the channel (salable_qty_seller = 7).

Is there any additional switch or internal lookup (e.g., a specific field in seller profile) our minor version expects so that the Cart sums the seller stock instead of returning 0?

Any pointer/snippet would be highly appreciated. Thanks a lot!

Notes

We’re currently using the core fallback so store can sell normally; looking to remove it once we align the Marketplace Cart expectations.

Thanks!