LaTeX Error: \mathrm allowed only in math mode

This error appears when we use a font in text mode which is only allowed in math mode. When using such fonts, ensure to include them inside dollar signs as $...$. To learn more about mathematical fonts, feel free to check out our documentation. A list of such fonts, with their corresponding packages is shown below

\mathnormal{...}	This is the standard italic font in math italic font. $\mathnormal{Hello world}$ will give the same result as $Hello world$.
\mathrm{...}	This is the standard text Roman font.
\mathbf{...}	This gives bold letters in math mode.
\mathcal{...}	This is a special calligraphic font in math mode. It can be used for uppercase letters only, such as for identifying real numbers. \mathcal{R} will give ℝ.
\mathsf{...}	This gives sans serif letters in math mode.
\mathit{...}	This will give text italic letters. These can be different to math italic letters depending on the specific class used.
\mathtt{...}	This gives upright letters from the typewriter type font used.
\mathbb{...}	This provides a "blackboard bold" font for uppercase letters. The amsfonts package or equivalently The amssymb package must be loaded to use this font.
\mathfrak{...}	This provides Gothic letters in both upper and lower case. The amsfonts package or equivalently The amssymb package must be loaded to use this font.
euscript	The euscript package provides us with another calligraphic alphabet called Euler script.

Text equivalents of the above math fonts:

Math mode font	Text Equivalent
\mathnormal{...}	\textit{...}.
\mathrm{...}	\text{...}
\mathbf{...}	\textbf{...}.
\mathcal{...}	No equivalent text mode font.
\mathsf{...}	\textsf{...}.