Earlier quoted context omitted.
This wasn’t the authors fault at all. It’s 2022, not 1998. I would expect a banking/payment UI to be very clear and foolproof.
I am not sure how much clearer "Your deposit exceeded the limit. The excess funds will be returned" could be.
As someone who has experience with savings bonds and Treasury Direct, I still have no clue how to interpret that phrase. Savings bonds are discrete things with discrete values, even though TD has worked to smooth over that quality with arbitrary purchase amounts and partial redemptions. "Excess purchase" may very well mean a refund of the entire singular $9,975 bond that was purchased.
The way to find out is to call TD or search around web forums, but it's understandable that OP reacted to one possible implication of the message rather than taking a few hours to find out what it means.