Invalid FEN help

I am having a problem entering FENs into the chess.com analysis board. 

On chesstempo.com, many of their FENs for the problems look something like

rn3r2/pbp2pk1/1p2q2p/3pN1p1/3P4/2NQ2PB/PP2P2P/5RK1 b - - 0 0

If I put this into the "Enter FEN" section, I get an invalid FEN error. However, if I change it to

rn3r2/pbp2pk1/1p2q2p/3pN1p1/3P4/2NQ2PB/PP2P2P/5RK1 b - - 0 1

I don't get the error anymore. Is there a reason why having a FEN end in 0 throws an error?

According to https://en.wikipedia.org/wiki/Forsyth%E2%80%93Edwards_Notation the last digit should be 1 or above, so maybe the problem is at chesstempo?

Thanks. It must be this. 

In addition to that, it's worth knowing that if you paste what chess.com itself produces when you ask it to *save* a FEN, you'll get "invalid FEN". For example, this...

[Site "Chess.com"]
[Result "*"]
[SetUp "1"]
[FEN "3rr1k1/3q1pbp/pP4p1/8/3p1B1P/5QP1/5PK1/1RR5 w - - 0 1"]*

...will get rejected. What you have to do is paste just the part within the double quotes, i.e.

3rr1k1/3q1pbp/pP4p1/8/3p1B1P/5QP1/5PK1/1RR5 w - - 0 1

(and — note well — without the quotes).

What's the difference between FEN and PGN anyway?

pgn is movelist

Essentially, FEN is a screenshot, PGN is a video.

pgn is the notation of chess moves and what format is used to display a chess game or diagram with many moves. Conversely, fen is the way of recording only one position. Almost a year ago, I made a video on fen. Maybe I'll revisit this topic with an improved video though. This was one of my earlier videos when I was starting YouTube.

At the very least, this explains what each digit of the fen string indicates.

So, I'm trying to make a video, and I set up the position to play against my alt, but then it just denies, and if I enter the FEN chess.com gave me:

7k/8/8/1R3p2/3QnPp1/3R2P1/6K1/8 w - - 0 1

It's an error and not a correct FEN, what should I do???

You need to insert a pgn, not a FEN. And this FEN is pretty valid.