CH155516 - Penalties for failure to pay on time: rules for specific taxes: Plastic Packaging Tax (PPT): penalties – failure to pay all or part of amounts due – further penalties
If any amount remains unpaid 5 months after the penalty date, the person is liable to a 5-month further penalty of 5%, as well as any initial penalty that they have already incurred.
If any amount remains unpaid 11 months after the penalty date, the person is liable to an 11-month further penalty of 5%, as well as any initial penalty or 5-month further penalty that they have already incurred.
See the example at CH155518.