The steps for opening a merchant payment code on JD.com are as follows:

1. Log in to the JD merchant backend using a JD merchant account. In the merchant backend, find the relevant payment settings entrance in the menus such as "Transaction Management" or "Payment Settings".

2. On the payment settings page, select the option to activate the merchant payment code. Depending on the JD platform, some relevant information, business license, etc. will be required.

3. According to the prompts on the page, fill in the necessary information and submit the application. After submitting the application, the JD platform will review it. If the application is approved, you will receive a notification and successfully activate the merchant payment code.