Welcome to Algorand!
It is possible to create an NFT on TestNet.
It looks like you may not have defined the suggested parameters correctly.
You can see there Create an NFT - Algorand Developer Portal
a link to a full REPL that works: CreateNFTJavaScript - Replit
I’m guessing you miss something like the line:
const params = await algodClient.getTransactionParams().do();
You may even just be missing the await.