I see that Brentford rejected Manchester United bid to sign Mboymo, I don’t know the reading for the rejection but I am sure it is because of money, maybe the amount is too small because Brentford like selling their players expensive, although the player is a good player and can help Manchester United especially with goals because he already have Premier League experience and will not struggle to adapt to Manchester United’s style of play.

Brentford rejected MU's first offer, yes that's true. However, they receive another bid, which is getting improved from the first bid. They wanted MU to increase their bid, and they receive what they wanted. No reason not to call no to MU's offer as long as it's meet their asking price.
I have no clue what happen behind the scene, but i believe the talk is still ongoing between them and MU's representative. I hope an announcement to be rolling out in the coming days.
Even there is a rumor says a medical check up booked for Mbeumo.
Seems quite tough negotiation between Manchester United and Brentford for signing Bryan Mbeumo, recently Manchester United have multiple bid for signing Bryan Mbeumo from 50 million euro and last bid increasing up to 60 million euro but Brentford likely want higher big amount transfer for his favorite players. Lets waiting the end of quite tough drama negotiation will Manchester United success get Bryan Mbeumo's sign b increasing their offer or Brentford will accept last bid around 60 million euro.
Last season, Bryan Mbeumo performed quite well by scoring 20 goals and contributed 7 assists, I think its right players for central forward and Manchester United have huge ambition how to get deal agreement with Brentford. Finally quite though negotiation will announce until early of next month before Manchester United will prepare for pre season matches.