QB Issue Resolution:
Sorry that functionality is not available for Mac users. You must go to the register and uncheck every item that appears on your last bank statement.
Resolution for Issue 'Undo previous bank reconciliation.' available: Yes (Solved).
Source: Intuit Community forum.
Undo previous bank reconciliation.: this 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 issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.Support for Banking
Quickbooks Repair Pro will resolve it efficiently and affordably. Guaranteed resolution of your issue, or you pay nothing!
Error Recovery for Banking [Canada]
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