Need to make changes to an invoice you have already synced or re-export?

In your Accounting Package
Ensure sure there is no payment applied to that invoice - simply
a) Remove the payment, then wait to reapply and reconcile until you have synced the updated invoice back.

In ConnectWise
1. Delete the batch record:
a) Go to Finance > Accounting Interface > Open Batches > search for INV1234 or INVXXXX etc,
b) Select that record
c) Delete that batch record  (NOTE: don't Close it - that will lock the record, a feature only used after a quarter or Financial Year is finalised)

2. Edit the Invoice
a) Go to Finance > Invoice Search > find the Invoice
b) Change the Status to Redo or Review (or your open status that will allow editing )
c) Update Product or TIme Entry or Billing Rate or apply an adjustment like a discount etc
d) Save
e) Resend invoice to client (optional)
f) Change Status back to Closed - Emailed (or whatever your Closed status is)

3. Resync the updated Invoice
a) Go to back into the integration tool retrieve data again.