math/unknown-label

An \eqref, or an Org \ref, names a Label that no numbered equation in the Entry has.

Example

$$\begin{equation} E = mc^2 \label{eq:energy} \end{equation}$$

By $\eqref{eq:enrgy}$, …

Fix

Use the Label the equation has, which the help suggests when one is close, or give the equation a \label.