Has anyone had to sign a form from Mouser before an order was allowed? (Nucleo Board)
This board is listed on their website with an EAR (Export Administration Regulations) due to it contain ART Accelerator. If you really live in the United States, this shouldn't trigger it. But probably they flagged you for some unknown reason that could be shipping to a hotel address, or not US issued credit card. It's impossible to know and they probably will never say why you were flagged.