MarketplaceId should be a positive number issue - help please!

Hi everyone - I wondered if there is anyone that can please help! I am listing my first product on Amazon and I keep getting the below error and I can’t figure out how to fix it! I tried researching, and You Tube. Does anyone have any ideas on what I need to do? Any help would be much appreciated!

Issue translator library encountered a technical error. The error was of type: MarketplaceId should be a positive number. Investigate using internal tools.