Unauthorized WOPI host. Please try again later and report to your administrator if the issue persists

installed Nextcloud 13 and setup collabora on docker (ubuntu16.04). All are working good. but the issue is when i try to open any odt or xls file it give an Error for " Unauthorized WOPI host" .

i have done nextcloud 13.1 and 13.2 but the same error i am getting. So please help me this out. I dont know what kind of issue is this. Please Help.