During your trial period, you can switch from the Flexible Plan to the Annual Plan and back. However, you cannot switch from the Annual Plan to the Flexible Plan during your subscription period. If you have selected the Annual Plan, you must wait for your renewal date to change your billing plan. If you have selected the Flexible Plan, you can switch at any time.

After your trial period, you can switch from the Flexible Plan to the Annual Plan by following these steps:

1. Sign in to the Google Admin console. 
2. Do one of the following:
   • In the classic Admin console, click Domain settings tab, then click either Subscriptions and billing or Billing information (depending on your billing system).
   • In the new Admin console, click Billing.
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3. Click on the [+] to expand your Billing Details
4. Click the change link next to Payment plan: Flexible plan
5. Select Annual Contract
6. Click Continue and review