The post link works for me in Firefox, Vanadium (degoogled Chrome), and WikiReader. The link in the post body gives the error described.
It looks like the post formatting is reading the URL as an unescaped string and escapes the percentage marks that already did that in the string.
The post link is: https://en.wikipedia.org/wiki/Ramanujan%E2%80%93Sato_series
But the version in the body is this: https://en.wikipedia.org/wiki/Ramanujan%25E2%2580%2593Sato_series
So yeah, it looks like it got double-escaped somehow.