This error occurs if you are trying to send multiple settlements to Xero at the same time.
Xero has a limit on how much data it will accept via its API per minute and so this error means Xero is throttling the amount of data we can send it.
To resolve this error try sending the affected settlements one at a time instead, or set up the auto post feature to send them across in a steady stream automatically.
👉 Tip: You may want to double check that some or parts of the settlements (if split-month) have not already been sent over by checking your draft invoices and bills folder, then delete them and try sending the settlements again one by one.