UPD. The problem is solved
Need to add verification code from the payment system <meta name="verify-bank" content="lotsofsomesymbles"> Prestashop 1.7.7.1. Tried to add in the head.tpl (themes/mytemplate/_partial ) the lines
{literal} <meta......>{/literal} - this didn't work
{block name='head_verification'} <meta=...> {/block} - neither this one
The code doesn't appear in the head. Would appreciate any help.