Ensure your base game NSP and the DLC/Update files share the same region code (e.g., USA, EUR, or JPN). Mixing regions will result in the DLC failing to activate.
: Connect your Switch to your PC via USB-C. Open DBI , select Run MTP Responder , and drag your NSP files into the "NAND Install" or "SD Card Install" window on your computer. Sonic Origins Plus Switch NSP UPDATE DLC