Expose my xibo docker to outside

I have built the Xibo docker and exposed it to outside via docker ports. Moreover, we have a firewall in our network. I can access the cms from outside (non-local network), even the Xibo display client can register itself in the cms and get authorized. However, it’s not able to fetch the layout from cms, and the client stock in Xibo logo (layout loading page).
Do you have any idea why this keeps happening? Is there any specific PORT or PROTOCOl which I should permit in the firewall?!

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