He was asking to have the loan sent to the same address he posted 1.5 years ago. I don't think I understand the logic in asking for a test transaction out of the address you are sending the loan to.
Just to let you know the logic:
The OP first had a different BTC address where 2double0 wanted the loan to be funded, which was bc1ql4gn6r75sydqwe99qz6nc44mvkzcfc4hqwqn3y posted by him
here.
So, I asked the test transaction form the Old BTC address as he needed the loan to be funded to a new one. But later he said he can accept the loan on the old one too so sent it there by confirming the address once.
But later the OP of the thread was edited by 2double0 with the old BTC address confirming his access to it by sending me a small amount of BTC.
Also, as an FYI, it is possible to sign a message from an address in a blockchain.infocom wallet -- you would need to export the private key, or xprivkey via the console then import it into a wallet that can sign messages, or at least this was the case in the past.
I know that and have a more better and easy method than this to get private keys from blockcahin.com. You just need to set a PassPhrase to your wallet on the blockcahin.com. Put you're pass phrase on
BIP 39 Mnemonic Code and you will easily get private keys to all the BTC address linked with your blockcahin.com wallet and later you can sign a message with the Private Keys for sure. Hope this helps you.

But 2double0 just sent me some minimal BTC from the Old address which made the deal quick.