Step 1: Go to the sandbox page. Step 2: Refresh the page. If this step is not completed, proceed to the next step. Step 3: Turn off Wi-Fi or any network connection, then click on the sandbox. You will see an error on the sandbox page along with an "Add Test Account" option. Click the "+" button to open the Add Account modal. Next, turn on Wi-Fi or the network connection while submitting. You are good to go!