In the Midtrans portal (Merchant Administration Portal), do these steps below:
1. Open Account > User Management menu, in the Create New User section, fill in the Name and Email Address the check the Activate Account.
2. Choose the user role, then click Create User.
3. Activate that user with click the link that is sent to that email.
Note: that process above can only be done by the user that role is Admin.
After clicking the link sent by email, the user will be redirected to a page that has to be filled. Please fill the Telephone, Password, and Password Confirmation field then click Sign Up.
The new account has been created successfully and can be used for login.
Note: make sure the telephone number is never used in the other Midtrans accounts.