If I explain to you how it all happened, it would get long and complicated, but basically, I forgot my wallet at home, so I can't pay this extra fare.
ご質問ありがとうございます。
"If I explain to you how it all happened,"=「もしあなたに、どのようなことが起きたかを全て説明するとしたら、」
"it would get long and complicated,"=「それは長くなって複雑にもなります、」
"but basically,"=「でも、要するに」
"I forgot my wallet at home,"=「私は家に財布を忘れてしまいました、」
"so I can't pay this extra fare."=「なので、この乗り越し料金が払えません。」
ご参考までに。
It's a long story, but basically I forgot my wallet at home and I don't have money to pay for the extra fare.
To make a long story short, I left my wallet at home so I can't pay the extra charge for the train.
この場合、次のような言い方ができますよ。
ーIt's a long story, but basically I forgot my wallet at home and I don't have money to pay for the extra fare.
「話せば長くなるけど、つまり家に財布を忘れて、乗越料金を払うお金がないんです」
it's a long story で「話せば長くなる」
basically で「要するに・つまり」
ーTo make a long story short, I left my wallet at home so I can't pay the extra charge for the train.
「手っ取り早く言うと、家に財布を忘れてきて、電車の乗越料金を払えないんです」
to make a long story short で「手っ取り早く言うと・かいつまんで話せば」
ご参考まで!