Oops! Noob mistake.
I thought that testnet and regtest had different version prefixes (not compatible) but they are (the bitcoin wiki and bitcoin developers page doesn't clarify this, though). So I went into a npm package that added dogecoin and litecoin testnets compatibility with bitcoinjs-lib (it's called bitcoinjs-testnets).
But the solution in the second Github link that I posted works.
Here I repost the text:
Just want to give some feedback that may help new users in the future.
I lost a lot of time debugging an issue that is probably extremely
obvious to some, but it was not directly obvious to me.
var bitcoin = require("bitcoinjs-lib");
var keyPair = bitcoin.ECPair.fromWIF("mywif", bitcoin.networks.testnet);
var txb = new bitcoin.TransactionBuilder(); txb.addOutput("myaddress", satoshis); // <---- this will fail with "has no matching Script"
Because of the error message I came to the conclusion that I was doing
something fundamentally wrong creating the transaction. In the end, it
turns out I just needed
var txb = new bitcoin.TransactionBuilder(bitcoin.networks.testnet);
Feel free to close this, just wanted to share my experience
I wish my noob experience has helped you! (pardon for my english).