No, it is not mandatory to enter a domain when configuring a hotspot in MikroTik RouterOS. However, specifying a domain can be useful for managing access and navigation within the hotspot network, especially in environments where you want to provide a custom login page or redirect users to a captive portal.

When you configure a hotspot in MikroTik, you can specify several parameters related to redirecting users to an authentication page, and one of these parameters can be the domain.

If you decide not to use a domain, users can be redirected using the router's IP address. This is common in simpler setups or smaller scale networks.

Using a domain makes it easier for users to remember and access the login portal, especially if the domain is intuitive and relevant to the service being offered.

Additionally, using a domain can help in configuring SSL/TLS certificates to improve hotspot captive portal security.