Can't get into each others world using Windows 10 and a Nintendo Switch

I am using the bedrock edition on my PC and my son is trying to join my world on his Nintendo Switch but it keeps saying unable to join world. I can't join his world either. we have Nintendo Switch paid accounts and Microsoft accounts. Others have been able to join my world and others have been able to join his world (using a PS3 and a Windows 10 PC) We can both play in a realm together.