problem.ts

// Global payload
interface Global {
    myGlobal: string;
    myOtherGlobal: string;
}

// Type with all global keys
interface Schema1 {
    schemaId: 'schema1';
    payload: {
        myGlobal: string
        myOtherGlobal: string;
        custom1: string;
    };
}

// Type with only one global key
interface Schema2 {
    schemaId: 'schema2';
    payload: {
        myGlobal: string
        custom2: string;
    }
}

// Type with the other global key
interface Schema3 {
    schemaId: 'schema3';
    payload: {
        myOtherGlobal: string
        custom3: string;
    }
}

// Type without global key
interface Schema4 {
    schemaId: 'schema4';
    payload: {
        custom4: string;
    }
}

// Union type (I can't really change this)
type Schema = Schema1 | Schema2 | Schema3 | Schema4;

// New union type without global key in the payload
type NewUnionTypeWithoutGlobal = ???

// Basic usage without any global key in the payload
const schemaWithoutGlobal: NewUnionTypeWithoutGlobal = {
  schemaId: 'schema1',
  payload: {
    custom1: string;
  }
}

// Usage when we can redefined some global keys if we want
const schemaWithOverriteSomeGlobals: NewUnionTypeWithoutGlobal = {
  schemaId: 'schema1',
  payload: {
    myGlobal: string;
    custom1: string;
  }
}

// Should not work because the schemaId doesn't match the payload.
const schemaWithOverriteSomeGlobals: NewUnionTypeWithoutGlobal = {
  schemaId: 'schema2',
  payload: {
    // Payload need to be grouped with the good schemaID
    custom1: string;
  }
}