Survey not merging

Version 7.10.7

I’m trying to send a survey campaign

I created a survey.
Create a Survey campaign.
When i get to the templates tab to insert the Email variables
choose survey and URL then insert
It shows $surveys_survey_url_display on the template
finish the survey campaign
Then send the survey campaign to a contact to see the outcome.
I see the same $surveys_survey_url_display in the contacts mail.
the variable doesn’t change to the value.
the link is not provided for the receiver of the emails

Any fix for this? Thanks!
i refer to the above issue
there’s no log written in the suitecrm log when sending these mails

Can you check also php_errors.log, or whatever your web server log is called?

And maybe increase your suitecrm.log log level in Admin / System settings.