Download FocusFrog for free from the Apple App Store.
Open FocusFrog and go to Settings → Integrations → Todoist.
Open Todoist in a separate tab and go to Settings → Integrations to find your personal API token.
Copy your API token and paste it into FocusFrog, then tap Connect.
Your Todoist tasks will appear in FocusFrog. Attach any task to a focus session and start your timer.