Background
This feature would enable the automatic execution of self billing documents for Self Billing with Automatic Posting (SBWAP). It avoid the delay in processing self billing documents which are within the defined tolerance limits. Help supplier claim the payment and report the tax to tax authority in time.
Solution
SAP Self-Billing Cockpit enables the option to configure automatic execution at "Define Sold to Party Parameters" application.
This configuration avaiable both for Self-Billing with automatic posting and invoice creation.

In case the self-billing documnet is not difference or the difference with tolerance. System would execute the self-billing document automatically.

Blog Post Series for SAP Self-Billing Cockpit