Why can orders not be created in Opencart?

Question

opencart

The manager complained that the client could not place an order on the site and tried several times .. he placed the order and nothing happened, even the letter did not come to the post office. I made a trial order, you never know. And between my and the last order, two IDs were missed, i.e. the last one was 161, and mine was 164. The database also has missing records in the oc_order table. Who faced?