Unable to send email quotes

Greetings,
I have stumbled upon a problem with email sending in your plugin. The email itself is working as intended, and I used both plugin and api in order to get wordpress to send them. Unfortunately, none of them work.
My current wordpress version is 5.4–ru_RU.
If there is any additional info, that is needed in order to identify the issue, I will be happy to provide it anytime.

The page I need help with: [log in to see the link]