QB Issue Resolution:

If the amount ‘owing’ is for prior period returns that have already been filed then its probably just an opening AP – not a GST adjustment. When you ‘file’ a GST return QB creates an AP to CRA.

Resolution for Issue 'I’m trying to adjust the opening balance for GST remittances – we started using desktop as of Jan 1 2019 but have a balance owing from 2018' available: Yes (Solved).
Source: Intuit Community forum.

I’m trying to adjust the opening balance for GST remittances – we started using desktop as of Jan 1 2019 but have a balance owing from 2018: 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.

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