Invalid AJAX response

#1

Can’t upgrade my new install of a grav skeleton because of “Invalid AJAX response.” also this pops up then: “Error while trying to download (code: 0): https://getgrav.org/download/core/grav-update/1.6.3 Message: URL using bad/illegal format or missing URL”
Same with theme installs.
What am I doing wrong?
I’m on Hostens shared hosting.