curl --request POST \
  --url https://api.uniblock.dev/uni/v1/json-rpc?chainId=bitcoin-testnet4 \
  --header 'content-type: application/json' \
  --data '{
    "id": 1,
    "jsonrpc": "2.0",
    "method": "combinerawtransaction",
    "params": [
      []
    ]
  }'

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": ""
}