The BrandMeister Manager is only visible when a BrandMeister server is selected in the Homebrew/MMDVM connector.
If you can't connect to a BM server then you are probably using a wrong server password. Please take a look at this post:
https://news.brandmeister.network/configure-a-security-password-for-your-hotspots/
You need to check the hotspot security setting on your BrandMeister SelfCare page at
https://brandmeister.network/
If hotspot security is turned on, you have to use the hotspot password you've set there as the server password in the openSPOT. If hotspot security is turned off, then you have to use the default server password which is "passw0rd" (without the double quotation marks). Note that servers nowadays usually require a hotspot security password to be set and enabled.