Contact Form 7 stopped working

Hi there,

Form 7 was working OK but it has stopped working. I’ve added DMARC authentication as per below ling which was the one thing that received a warning when sending a test email.

https://wpmailsmtp.com/how-to-create-dmarc-record/#check-dmarc

Whenever I try to send a test message I get a circle going around and so never get the email, errors that I get as follows:
Event #17 Error Mailer: Other SMTP SMTP Error: Could not authenticate. WP Mail SMTP September 30, 2021 at 8:14 pm
Event #16 Error Mailer: Other SMTP SMTP Error: Could not authenticate. WP Mail SMTP September 30, 2021 at 8:12 pm
Event #15 Error Mailer: Other SMTP SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshootin… WP Mail SMTP September 30, 2021 at 8:11 pm
Event #14 Error Mailer: Other SMTP SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshootin… WP Mail SMTP September 30, 2021 at 8:10 pm
Event #13 Error Mailer: Other SMTP SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshootin… WP Mail SMTP September 30, 2021 at 8:09 pm
Event #12 Error Mailer: Other SMTP SMTP Error: Could not authenticate. WP Mail SMTP September 30, 2021 at 8:08 pm
Event #11 Error Mailer: Other SMTP SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshootin… WP Mail SMTP September 30, 2021 at 8:07 pm
Event #10 Error Mailer: Other SMTP SMTP Error: Could not authenticate. WP Mail SMTP September 30, 2021 at 7:50 pm`

Site went from staging to production and I tested in production and worked both – sending a test email within WP email and also filling out a form on the live website after it came to production – I click on “Event” log and I get the following on some of them:

Source
WP Mail SMTP
/var/www/vhosts/staging.mydomain.com/httpdocs/wp-content/plugins/wp-mail-smtp/src/Admin/Pages/TestTab.php (line: 314)

Any input here on what may be causing this?

Many thanks.