Please read this article first. Then see the steps below.
Step 1: add your Todoist address* in Braintoss. Go to settings and then click on “add e-mail address”. Paste your Todoist address here.
Step 2: if this Todoist address is your default address in Braintoss, it will automatically send to this Todoist address. If you have multiple email addresses in Braintoss you can select the email address by holding the “+” button before sending.
*You can find your Todoist email address in each project. Open Todoist, go to a project, click on the three (3) dots in the upper right hand corner, click on Email tasks to this project and you will see the email address. Only via online, not in the Todoist app.
For more information: https://todoist.com/help/articles/forwarding-emails-to-todoist