You may find more info, how to setup Paysera payment gateway in Ecwid if you open the link below:
https://support.ecwid.com/hc/en-us/articles/207099949-Paysera#set-up-paysera-in-your-store-0-1
Additional information:
* Please place the Paysera logo in a prominent place of your website, such as the footer. The Paysera logo can be downloaded in various formats from HERE.
* Add additional host to your Paysera project URL list, which is used by Ecwid system: https://paysera.ecwid-labs.com