"It's not a case of we sign the contract and they go and raise the money. If you've got it - show us it and then we can talk," Hearn, who is in New York for a Matchroom Boxing USA card and will meet Wilder's representatives on Friday, said.
Wilder's promoter Shelly Finkel had earlier given Joshua until midnight on Thursday to respond to the offer.
"I spoke to AJ, he knows the situation but we want to know if it's real," Hearn added. "We want to see the money and know where it is. There is a real strong chance this fight could happen - we're not looking to be difficult."
However, Finkel said the money was in place. "If he accepts it, it will be there. Al Haymon and I have never not delivered what we've offered," he said.
Joshua last month moved a step closer to becoming the undisputed heavyweight champion of the world after beating New Zealand's Joseph Parker in their title unification bout to improve his record to 21-0.
The 2012 Olympic champion added Parker's WBO belt to his own collection.
(Reporting by Shrivathsa Sridhar in Bengaluru; Editing by Toby Davis)
