Invalid status code on Head request Issue

Hi, I am new to the ODK central, meanwhile, I was able to deploy central to the digital ocean cloud; I set everything including web user and app users, but unfortunately trying to submit a response in ODK collect come across this errors message: Invalid status code on head requests. if you have a web proxy you may need to log in to your network
I will be glad someone to throw more light on how to tackle these errors. I am sure that I am in the right place