Translation issue

Hi, nice plugin, really easy to use.

Im having localization issue, it want load the language file i created with poedit. I translate the .po file and set as fbsr-sr_RS and it doesn’t work. I also tried ipt_fbsr-sr_RS and ipt_fsqm-sr_RS (read on some manual) but non of them work also. Files are located in /public_html/wp-content/plugins/wp-feedback-survey-manager/translations/. What im doing wrong here?

Thanks

https://wordpress.org/plugins/wp-feedback-survey-manager/