A treatment can be deleted once the money has been un-allocated from the treatment.
The below article provides the steps on how to do this.
Once the money has been un-allocated from the treatment you will be able to delete the treatment via the 'Treatment' section.
Alternatively, the treatment can be deleted by following the below steps:
Go to 'Patient' > 'Financial' > 'Purchases' > Select the bin to delete. See below: