in or bei
Which is the correct alternative and why?
They are both the same correct.
Checking some other sentences you will see that in and bei are used similar in cases where the Englisch original is for and in (or may be at)
here are examples for
in dringenden Angelegenheiten:
https://www.linguee.de/deutsch-englisch/uebersetzung/bei+dringenden+angelegenheiten.html
https://www.linguee.de/deutsch-englisch/uebersetzung/in+dringenden+angelegenheiten.html
however looking up right your question there are 4 examples with bei and only one using in.
You can look up LINGUEE English-German and you won't find a difference in use or semantic meaning, while there may be a statistic preference of the use of bei
Don't break your head any longer.