When setting up TRONC payments in BrightPay, make sure a separate PAYE scheme is in place for TRONC, as this is how HMRC will identify and process it.
There is no way to instruct BrightPay that it's a TRONC payroll however, you will have to ensure the correct treatment is applied to the payments manually.
After that, you can run payroll as normal and record the TRONC payments as taxable but not subject to National Insurance. These payments should be entered manually under the Additions and Deductions section, allowing you to apply the correct settings. Please note that BrightPay does not automatically recognise or apply TRONC-specific rules.