When you sign up for a Google Cloud free trial and receive the $300 credit, that credit is meant to cover eligible usage charges for Google Cloud services. The free trial credit will be applied to your billing account, and any eligible usage charges you incur will be deducted from that credit until the credit is exhausted or the trial period ends.
If you decide to register a custom domain through Google Workspace (formerly known as G Suite), the cost of the domain registration is typically not covered by the Google Cloud free trial credit. Domain registration fees are separate from Google Cloud services charges and are generally billed separately.
Therefore, it's likely that the $12/year for the custom domain registration will be charged to the payment method you provided when setting up your Google Workspace account. The $300 credit should only be applied to charges related to eligible Google Cloud services and products used within the free trial period.
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