What kind of high fee are you talking about?
Bitcoin transaction fees have been at their lowest level for a long time, but at 1-3 sat/vB, you can't expect anything less. It was the same when you started the campaign.
You need to post the address (signed) where the funds for the campaign payment are held.
I assume he doesn't even know how to send a batch payment. So he is right when he said he wants to avoid high transaction fees. I assume he received the signature payment in his Binance account, and if he sends payments to participant one by one from the Binance account, he will have to spend a lot in fees. So, he is collecting TRX address instead. I am telling this based on his previous action. According to some of his previous campaign participants, he sent payments via Binance pay ID to his participants. I don't think he will be able to sign a message from the address since he may received it in a exchange address.