Hello! 
Yes, we can guide you with connecting MailerSend using the API connector.
Once you’ve added the API name, you need to set the Authentication to “None or self-handled” and then add the following shared headers:
Key: Authorization
Value: Bearer {Your MailerSend API Token}
Key: Content-Type
Value: application/json
Key: X-Requested-With
Value: XMLHttpRequest
If you’re adding a call to send an email, make sure you select the Data type as “Empty” otherwise you won’t be able to initialize the call.
We hope this helps!