insert statement conflicted with the foreign key constraint

hello uhm i wanted to test the app for Todo but when i try saving the Todo it gives me this error  can anyone help me solve this problem please"

This is a database error. You're trying to create a record (Post) with an invalid UserId. The Foreign Key in this column/attribute doesn't let you enter values not matching the User table/entity.

Review/debug your logic in order to find out why UserId has an invalid value.

Hello. How did you get the Todo app? Did you create it?

This error is a database error. Most likely, you're trying to insert a row in the database without having a UserId, but the attribute is mandatory.