Castinvalid error(Could not cast from Number (Integer) to MY CDT.

You cannot convert a number into a data structure with multiple fields. How should Appian know where to put the value? What do you want to achieve?

You cannot cast a Number/Integer (a single value) to your CDT (which contains 3 mapped key-value pairs). Invalid conversion. Appian Docs has a section about Casting; can also look at Appian Functions under Quick Links (top navigation bar).

You cannot convert the integer value to a CDT, but you can map the value to a field in the CDT (like the 'id' field). Example below. When you do it, you would want to type in: type!RB_Test. It should pop up with autofill that looks closer to below. When you put the cursor inside the parenthesis at the end of it, on the bottom left of that screen, it will show you the keys for that CDT.

'type!{urn:com:appian:types:RB}RB_Test'( id: ri!integer )     =>     TEST RULE     =>     RB_Test{ id: 100, name: null, memo: null }