Encountered ConnectWise PSA API 500 Error: Object reference not set to an instance of an object
This error can be caused by a few things such as not receiving any data from ConnectWise PSA or by a $0 dollar invoice. The 500 error is causing the whole batch to error out, however, the issue most likely lies with 1 or 2 invoices.
Do note that this error can happen with Expenses and Inventory/Procurement batches as well.
Locate the batch in recent batches and verify what type of batch this is (i.e. Inventory/Procurement, Expense, Invoice).
Navigate to the batch screen where this error is happening. Most likely there are several items on that screen to be batched. You will have to run each item separately to find out which one of the invoices is causing the error. The best way to do this is to first do all of the invoices with a positive or negative dollar amount. Once those go through, then go through the $0 invoices one at a time till you find out which one is the issue.
Once you find out which invoice is causing the 500 error, the fix is to delete the invoice, re-create it, and re-run the batch