Hi Galina! The two sentences are completely interchangeable. The only slight difference is that I, as a native speaker, may be more likely to say “it’s been so nice meeting you” if I truly got to spend some time with them (even if it’s just a couple hours over dinner or a single engaging conversation). “It was nice to meet you” works just as well for if you just briefly meet and exchange hellos or if you went on a multi-day trip and are parting ways. Does that make sense? Honestly though, they both work well and the difference is so slight that I wouldn’t worry too much about it. No one will look at you funny if you used either one :)

"It was nice to meet you." - this is a common phrase used at the end of conversation when two people are about to part company. "It's been nice meeting you." - this phrase is not used in everyday American English.

None. Both of these verb tense forms refer to the past. There is a very slight difference in meaning. To explain the difference, I'm going to be ridiculously precise. Suppose you had lunch with someone from 1:00 through 1:29 and then got up at 1:30 to say goodbye. "It was nice to meet you" means you are thinking of lunch as a single event. You are thinking of the number one: one lunch. And you are putting it entirely in the past. It included 1:00 through 1:29. It is now 1:30 and it is over. You are thinking of the number "one," one lunch. "It's been nice meeting you" means you are thinking of a period of time, 31 minutes, 1:00 through 1:30. Although you are at the very end of the period of time, it is not quite over. To me "it's been nice meeting you" is a little friendlier, because the "nice meeting" is still happening, whereas "it was nice" means it is over. I'm not a grammarian and had to look up the names, but that's the difference between the simple past tense ("it was") and the present perfect continuous ("it has been.")