I'm reading guides on the internet involving another wallet but maybe it could also work in your case. Let me get this straight, your HT (erc-20) is sitting in you metamask wallet and you just added the heco-mainnet right?
Can you try the following and see if it works?
1. Create a new metamask account maybe in another browser
2. Add the heco-mainnet
3. Under heco-mainnet, import your wallet containing your HT.
....
No Sir, RPC URL address is invalid.
The RPC URL is valid. It's probably a copy-paste issue which made it invalid on your end.