How to solve a status 308 with Action Mailbox?

Hi !

I am trying to send email from my Gmail accounts to my Rails application using Action Mailbox.
To configure it, I've followed this tutorial https://gorails.com/episodes/action-mailbox-rails-6?autoplay=1 and configured Sendgrid using this article https://adamnaamani.com/how-to-route-emails-with-action-mailbox/

Before pushing it to production, I've pushed it to staging on Heroku.
When I look at my logs, I can see the POST request with a status 308. I don't understand how did I get a permanent redirect status, and so where can I find the URL it was redirected to.

Do you have any ideas of what should I do ?

Cheers

Helena

It was because I was using http instead of https in my Sendgrid's url