MailPoet v. 3.47.9 issue with sending emails

Hi,
I’ve set up the plugin and SMTP gateway (checked with Check Email plugin). I can subscribe to the list. Confirmation email was sent, but the plugin doesn’t send welcome message (activated). There is message “Oops! There seems to be an issue with the sending on your website. See our guide to solve this yourself.” at the top of the page.
I used your solution to send emails and the email address is confirmed and the account is activated.
I can’t find any configuration mistakes. I went through your website tutorial and many others. Still nothing. Could you help, please?