Debug & Update Existing Flask Marketplace application

We have a Flask app which had a UI and feature update recently, the update has left a bug in getting the payment function (stripe payment) to not work in the shopping cart.

The application uses Flask blueprints https://github.com/Anioko/resuable-flask-marketplace. We would like to get the bug hindering successful payment sorted and a few other small issues to deploy the app. The shopping cart has already been developed, same with adding products.

In the marketplace there are buyers and sellers. A buyer can be anonymous. Seller can add products to the marketplace. A buyer cannot add products. The admin can make a user to become a seller. Sellers have different dashboards.

We also would like someone who could be available to enhance it further should we have new requirements, we would discuss and set it up as a separate task.

For this project we want the following:
- Current bug restricting completion of payment by the buyer, cleared to ensure buyer can pay for purchases in the shopping cart.
-Admin should be able to add product variants
-Make the Shipping methods of the seller should be the shown on the order area for the buyer to see.
- Product variants should be optional. It is not compulsory for a product to have a variant.

The end goal is to have the marketplace ready for both buyers and sellers to use successfully.

N/B
-Please if you have not worked on Flask and used Flask Blueprints please this requires knowledge of Flask.
-Please don't recommend or suggest that we start the marketplace from scratch. We will not change from Flask to Django or take up another marketplace CMS.