Hello Boyan,
Thank you for reaching out to our support team.
A 500 error during the preflight check usually points to a server configuration issue, but without the full error message, it’s hard to say for certain.
If you’re able to, please reach out to your hosting provider and ask if they can check the server logs for the specific error. Alternatively, you can enable WP_DEBUG in your WordPress site and try visiting the page again. If you’re able to share the full error message that appears, I’d be happy to take a closer look and help from there.
Thanks,
Elana