The free licence allows for a maximum of three employees per tax year (up until the 2018/19 tax year). The three employee limit includes both previous (leavers) and current employees in any tax year.
The free version of BrightPay does not include support for CIS (Construction Industry Scheme) or employee's Expenses and Benefits (including P11D). If you need these features, please purchase a Standard licence.
Also, free licence customers are not entititled to phone support – if you require phone support, please consider a Standard Licence.
If your BrightPay trial has expired, then when you launch BrightPay it will ask for a licence key – simply type or paste in your Free Licence key.
If your trial has not ended, then the licence screen can be accessed from the Upgrade Licence button on the welcome screen or from Help → Licence after opening an employer file.