Your download transactions should match the existing transactions in QB. Nothing should be duplicated unless you are adding transactions instead of matching.
Resolution for 'adding transactions issue: 'Customer Payments are duplicated by transactions downloaded from bank.' available: Yes.
The adding transactions issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the adding transactions issue yourself by looking for a resolution described in the article. If it is a complex adding transactions issue or you are unable to solve the issue, you may contact us by clicking here or by using other adding transactions support options.
For more information about resolving issues related to adding transactions in Quickbooks/QBO or to get support for the issue 'Customer Payments are duplicated by transactions downloaded from bank.', click the link below: