If your products show up as “Not available”, you're either using Free Weebly plan, or you've exceeded 25 product limit of the Pro plan.
If you’re using the Free plan, you can add as many products as you like, but they’ll show up as "Not available". To start selling, upgrade your plan to Pro (Professional in the US), Business (Performance in the US), or Business Plus (available in the EU only). To upgrade your plan, click Upgrade in your Weebly toolbar or your store dashboard.
Note that with the Weebly Pro plan, you can list a maximum of 25 products (each variant counts as a product). If this limit is exceeded, the products will show up as "Not available". With Business or Business Plus you can list unlimited products.