It says that the letter was sent, but the recipient did not receive it

Nadin

I sent a letter to this page https://lp.sales-****.ru/121

I went to the admin panel of the site and there is no received letter, although GSA writes that the message was sent

also when sending a letter to this form, it says that the form was not found 

https://wow.1kfu***.ru/cms/system/contact

and there is a form there

Sven

site 1: that submitted fine for me with a resulting {"message":"OK"} in source afterwards

site 2: that one had no contact form. It only shows due to javascript being executed.