New Sales Invoices
Create new for POS for Record Type = Parts.
Or created from a Sales Order for Record Type = Service or Trailer
POS Payment
Can be collected for all 3 record types, and for both invoice and credit memos.
For Parts, service, POS Amount must equal to the Remaining Amount
For Trailer, POS Amount can be less than the Remaining Amount
Exchange or Credit Memo
Apply the credit memo to an invoice first.
Then create a negative POS for the balance.