According to Pugmire, Wilder's and Joshua's respective teams were quibbling over the location of the fight, with Wilder's camp wanting it in the USA and Joshua's side preferring the UK. The ball is in their court.
Matchroom boss Hearn is believed to have made a counter offer, which would see Wilder challenge Joshua in his backyard and take home a smaller fight purse.
"We offered $50 million, which is what he said he wanted", Deas said to the AP.
Wilder offered up these comments as he confirmed he had agreed a deal to fight in the UK: "The $50m (£37m) offer for him to fight me in the U.S. is still available".
Wilder's manager Shelley Finkel separately indicated to World Boxing News on Monday night that October is an option as well as September, which would go some way to quell one of Hearn's concerns about a September date clashing with Canelo Alvarez's return from a drugs suspension. Deontay wrote to Joshua and said: "Hey, I accept your offer, let's fight in the UK". Shortly after, his co-manager Shelly Finkel confirmed to multiple sites that the offer includes a rematch in the United States.
Another possible outlet is the Perform Group's DAZN sports streaming service, which is due to launch in the US later this summer, with Hearn's recently agreed to eight-year, $1 billion deal to provide boxing content due to begin in September. Yet America's Wilder has been standing in the way of Joshua's complete dominance.
That offer did not meet the requirements of Joshua and Hearn, with the duo edging towards a fight against Russian contender Alexander Povetkin in recent days.
The WBC champion, Wilder is 40-0 with 39 knockouts.
The 28-year-old Joshua (21-0, 20 KOs) won a world title in 2016 and has made five defenses, including a 10th-round knockout of former longtime unified world champion Wladimir Klitschko in the consensus 2017 fight of the year and unifying three belts with the win against Parker on March 31. Currently, Joshua is a -200 favorite and Wilder a +170 underdog.