Hi @coryg,
only the older Mailgun accounts have the API key which starts with the “key-“.
My Mailgun API key also does not start with “key-” and the integration works OK.
Is this a brand new Mailgun account? Did you complete the account verification steps (verified email and your phone number)?
If it’s a brand new account and all the details are correct (API key, sending domain and the region), then maybe Mailgun hasn’t activated your account yet and is blocking any requests. Maybe it would be a good idea to contact their support and verify if your account is allowed to send emails via their API.
The only other thing I could advise is to re-check all the settings (API key, sending domain and the region). Maybe try sending with a different region.
You can see which region to use if you go to the mailgun sending domain list: https://app.mailgun.com/app/sending/domains and see which flag is next to your sending domain (US or EU). Use that region in our plugin and try again.
For example, I’m from EU, but my sending domain region is US. If I try to send emails with EU region selected in our plugin I get the same error as you do, so I think that’s what might be the issue for you as well.
Let me know how it goes.
Take care!
