How to use shopify order API if customer doesn't have shopify store

1 I have my own website , and there are 2 types of users: merchants (sellers) and customers (purchasers).

2 Merchant have a store on shopify for inventory management. I am able to get the products from shopify for my site.

3 Now I want to sell those products from my website using the API (https://shopify.dev/api/admin-rest/2023-01/resources/order#post-orders), but this API requires a shopify-access-token and my customer is not registered on Shopify.

4 Is it correct to use the merchant’s shopify-access-token in order APIs for customers?

Please let me know I am on the right path or suggest the correct way to complete my task.