It should be clear by just looking at the block explorer web page that a Bitcoin transaction has many different parts. Some parts are just small numbers and some parts are larger chunks of data. The Bitcoin protocol has a very specific algorithm for creating messages from transactions, so those messages can be signed by private keys.
We will summarize the process outlined here. It conveniently uses this exact same transaction as an example.
To begin, we need the raw bytes that make up the complete transaction. Our block explorer can help with this. Use the "hex" API endpoint and paste the entire blob of data.