"便利商店" (biànlì shāngdiàn) vs "便利店" (biànlì diàn) Earlier when I was in China I learned "便利店" (biànlì diàn) to mean "convenience store". I think from looking it up in the English Wiktionary.

But now that I'm in Taiwan when I used it people didn't understand it and then corrected me to use instead "便利商店" (biànlì shāngdiàn).

When I check on Google Translate it supports both.

So is this a PRC vs Taiwan difference? Or is it generational? Or are they straight synonyms?
It's a PRC vs. Taiwan thing. It's like American English vs. British English. You'll find many words are different in Taiwan.