Try each of the following steps in order until the issue is resolved:

1. If the import includes a Debit Transaction Distribution Project ID, add a column to the import file mapped to Debit Transaction Distribution Percent with a value of 100

2. Create corresponding Credit entries for the Debit entries:
For example:
If distributing to two Debit accounts at 25% and 75%, the corresponding entries for the Credit account (even if there is only one) must be made in the same way, 25% and 75%

3. If importing multiple line items with multiple distributions, it is necessary to use the recurring invoice line item import facility.