A Delimiter Error

Question

LaTeX indicates a delimiter error for the following written code. Please help me if possible.

    \begin{equation}
    \frac{1}{\sqrt{1-t^{2}}}\exp \biggl⁡[(z^{2}+z'^{2})+\frac{2zz't- 
    (z^{2}+z'^{2})}{1-t^{2}}\biggr]
    \end{equation}

Answer 1

There is a (invisible) Unicode codepoint U+2061 (FUNCTION APPLICATION) between \biggl and [. Remove \biggl[ and rewrite it.