GST370 Form is used to apply for the GST rebate. You could apply for a GST rebate if you are an employee, your employer is a GST registrant, and you paid GST/HST on certain employment expenses. For further details about GST/HST rebate, please check our TurboTax article: Did You Know You Can Claim The GST/HST Rebate On Your Expenses?
The amount in line 1 is the amount of GST you paid on eligible expenses. If you claimed employment expenses, your employer issued you a completed and signed Form T2200 – Declaration of Conditions of Employment Form, and you answered "Yes" to the question "Are you eligible to claim the GST/HST rebate", TurboTax will calculate the GST based on the rate of your province of residence.
For further details about eligibility and how to complete Form GST370, please check this CRA FAQ: Employee GST/HST rebate (CRA)
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