Authentication problem with data server. (401)

We have problems sending surveys on IPhone cell phones, I get the following message:
Authentication problem with data server. (401)
how can i solve that?

Welcome to the community, @gaba_sanjines! Could you share a screenshot with the community so that the community can also understand your issue pictorially? BTW, please be informed that the 401 error message refers to the client request has not been completed because it lacks valid authentication credentials for the requested resource.