Email Sending Issues

Hi,
I’m currently encountering issue sending newsletter to my subscribers.
Please see image below for the error message.
image

I already setup my mailgun under members page with apiKeys.
I’m using version 3.32 of ghost and currently have 1.6k subscribers.

I’m not sure what are the cause of the errors.

Im running 3.35.5 and Im also hitting the same issues.