It’s in the polymer money most countries are now using. Gelatin - pig.
https://www.theguardian.com/business/2017/aug/10/bank-of-england-to-keep-animal-fat-in-banknotes-despite-complaints
Bank of England to keep animal fat in banknotes despite complaints | Bank of England | The Guardian
Central bank says it will continue to produce plastic notes containing tallow because palm oil alternative is too costly
https://www.theguardian.com/business/2017/aug/10/bank-of-england-to-keep-animal-fat-in-banknotes-despite-complaints