problem in assigning OS server

Dear colleagues,

actually, I am using multi-project. and I am using this configuration for the project.

In my project, I have one RTX pcs7 box

one Engineering station / OS client

and one OS server

I can ping the plc and OS server from Engineering station and I have all the connections in the Simatic shell.

for the configuration, I want to assign the client to the os server but I can not select the right project from the checkbox and upload it. it's gray without any selection.

I have attached the screenshot of the project and the checkbox.

To solve this problem what should I do?

Thanks in advance