With effect from 23 Sept 2020, Xero Integration's help documentations will only apply to existing customers or prospects that have created trials before said date.
Go to My Apps> Xero> Ledger Accounts tab. Click on 'Add a Custom Ledger Account'.

On the same tab - Ledger Accounts, map your newly created ledger account to your Xero account.

Set up Default Sales Account
You can now set up your default sales account by choosing from 3 options:
- Company (Relationships)
- Variants
- Sales Channels.
To do so you have to go to your Settings > Configuration > Default Settings. You will see the following:

It is essential to set it up correctly because this is how your sales total will be tracked on.
If you do not see the option 'Default Sales Account On' in your Account Settings, it might be because your accounting integration has not been set up accurately.
Select the option you wish to use as default. For example, if you want Invoices from all your Relationships to go to Accounts Receivable, select 'Company' in your Default Sales Account On as show above.
However, if you wish to have Invoices created by a particular customer to be filtered, you will have to first create a custom ledger account e.g. VIP Customers, then go to the specific Relationship to change the Relationships> Default Settings > Default Sales Account.
Similarly, you can do so for Company, Variant, and Sales Channel by going to the default settings for the Relationship or default sales account by variants to specify that Invoices will be pushed to this custom ledger account.
Things to note 📝
Can I have different defaults in my account settings and my individual relationships/variants so that I can filter the sales invoices further?
No, it will not work. Do note that for this to work, you have to ensure that your "Default Sales Account On" in Settings> Configuration> Set up Defaults has to be the same as what you are selecting in the individual Relationship or Variant or Sales Channel. For example, if your Account Settings, "Default Sales Account On" is selected as Company, you will only be able to specify Relationships to push to your custom ledgers.
Conversely, if your Account Settings is set to "Default Sales Account On" for Variant, going to a particular Relationship and setting the default sales account for the relationship will not have any effect on Invoices created by the Relationship. This is because the Account Settings overrides the individual default settings in Relationships or Variant or Sales Channel.