Why is なんだって at the end of 「当日券は現金購入だけなんだって。」?

Question

Consider

当日券は現金購入だけなんだって。

They say same-day tickets are available for cash purchase only.

(Source: from a Tofugu tutorial on だけ)

Questions:

1. Is 現金購入 one word, or two placed next to each other appositionally? (Or maybe there's a の in between them that's being dropped?)

2. What is なんだって doing at the end of this sentence? I assume it's short for 何 + だ + 言って? If so, why put 言う in the て form at the end of the sentence (since this doesn't seem like it's a command)? Also what role is 何 playing here (given that this doesn't look like an interrogative sentence)?

Answer 1

1. 現金購入 is not an appositive construction. 'Cash' is not equal to 'purchase', right? 購入 ("～ purchase") is one of those words that can form compounds almost like a suffix (e.g., クレカ購入, 電子マネー購入, 定期購入). See the last part of this answer.
2. It's なんだ + って. See Chocolate's links.
   • なんだ (なのだ) is a plain example of explanatory-の.
   • って is a quotative particle that means "I heard" here.