my refund request was rejected.
Good evening,
You have recently requested a refund for an order you have placed for Avalon ASIC chips. Unfortunately, verification of your request has failed. In order to process the refund request, a message signed using the original sending address used in the transaction is required. Please submit the message "I am hereby requesting refund of payment for my purchase of Avalon ASIC chips from forum member Steamboat" without quotes using the following format:
Bitcoin sending address used for original purchase
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message
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signature
I sent BTC from coinbase directly. I do not see any kind of option to sign message

anybody have any ideas?
I know there is a
lot to read here, but I'm sorry to say you didn't follow the instructions in the OP:
*Note* Do not send funds from an address you do not control. You will be required to prove ownership of the sending address upon request.
If there is any recourse for you, I think it will have to be steamboat making a special exception. Good luck.