Why am I unable to generate a credit invoive?

Summary:

We are unable to generate a credit invoice for the credit expenditure cost item.

Content (required):

We billed the July 2021 expenditure item in August 2021. The expenditure cost item billed on that invoice was transferred from Project 1 to Project 2, which creates a credit expenditure item on project 1.

The transferred item was billed on the invoice for Project 2. Which now means we have invoiced the item on Project 1 and Project 2.

We are trying to generate a credit invoice for the credit expenditure item on Project 1, but we can't get an invoice to generate.

How can we resolve this issue, and generate the credit expenditure item on a credit invoice?