Very frustrating error, never happened before

I have several websites with licenses for Elementor Pro and have created enquiry forms for those sites. When a user clicks send, it redirects to a “Thank you” page with no issues.

The latest project has exactly the same process and form however, each time we click send, an red error message appears at the bottom of the form in red saying “x error”.

I have tried WP Mail SMTP in case there was an issue with the email, I’ve also tried fluentSMTP and that gives an error message in red showing “E87F error”

I am completely lost and somewhat frustrated with this as it’s never happened before.

Needless to say I’ve tried chatGPT to try and establish what the cause is, Googled etc but to no avail. There was suggestion may be a memory issue but the .htaccess and functions.php files have all been altered accordingly as per the advice but these have all failed.

Please can someone help me resolve this?

Thank you

Steve