Monzo Bank have implemented a limit on the transaction amounts per day. Thus, consecutive Token requests above this limit can cause transactions to be Rejected on the bank's side.
The payment limits represent the FPS (Faster Payments Service) limits on the PSU account. By default, Monzo bank accounts will have a daily limit of £10,000 and the FPS scheme supports up to £250,000.
If the user hits these limits then they will either need to wait until the next day or request a limit increase in the Monzo app.