I'm going to assume that you installed Tailscale on your
Blue Iris system. Try going into your phone, enable Tailscale on phone, bring up a browser on your phone, type in your Blue Iris Tailscale IP address. You may need to add the port onto the end of it (i.e. 100.xxx.xxx.xxx:81). If that doesn't work, try going to Blue Iris / Settings / Web Server, enter in the Tailscale IP address assigned to your BI system in Remote,external area, save, reboot.
As for using Tailscale locally (i.e. your iPad), don't use it....use the local IP address, as the Tailscale IP should be used only if you are remote.