Have you been putting ongoing spend on the SPG Biz since hitting MSR and getting the bonus? Or have you sockdrawered the card?
That pop up message means Amex has flagged you as, essentially, an unprofitable customer who might be only interested in chasing bonuses and not putting any ongoing spend on their Amex cards. It’s typically targeted at applicants who have signed up for Amex cards, met MSR, pocketed the bonus, and stopped (or perhaps dramatically dropped) spending on those cards. The only cure anecdotally is putting some spend on your existing Amex cards may get you back in Amex’s good graces, and get that pop up to go away. How much spend, and for how long is anyone’s guess. Keep spending and try applying again periodically until you don’t get the pop up. Some people have charged a $5 slice of pizza, tried again and no more pop up. Others have put thousands of dollars in new spend on their card(s), and still gotten the pop up. Maybe Amex has some sort of algorithm based on how deep in the hole you are with them. It’s certainly not any hard rule that’s easy to understand like 5/24.
ETA: You weren’t denied. That pop up message is a warning from Amex that you won’t get the welcome bonus, and gives you a choice whether to continue the app knowing you won’t get the bonus. You can still be approved for the card without qualifying for the bonus.