Hi, 

Until recently survey links sent to customers suddely reach a "not authorised" page. We have used Timba surveys   for the last 2 years and no issues and we have made no changes. 

Test survey link: https://firstbaseit.secure.force.com/timbasurveys__survey?cId=0031p000026g26x&id=a0m1p00000HFXc3AAH