Referencing equations not working?

Things I have tried

In this forum, although automatic numbering and referencing don’t work, there is a manual workaround as what follows:
$$e=mc^2 \tag{abc}\label{name}$$
You can now refer to this formula: $\eqref{name}$

But what I get is this… weird… Does anyone have the same problem?
Sometime the reference will be ???

What I’m trying to do

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.