Error: LOOK UP VALUE does not support comparing values

Hi all,

I found the above error when trying to create a calculated column using the LOOKUPVALUE function.

So I have the following tables;

Table C is a summarized table using columns from Table A & B and the Changes column is a calculated column. Ideally, Table C monitors changes between Table A and B. 

The dax code used to calculate the column "AMOUNT DIFF" is;

AMOUNT DIFF =

var tab1 = LOOKUPVALUE(Table A[ID],Table A[Amount], Table C[ID])
var tab2 = LOOKUPVALUE(Table B[ID],Table B[Amount], Table C[ID])

Return tab2 - tab1

I get the  ERROR: Function 'LOOKUPVALUE' does not support comparing values of type Text with values of type Integer. Consider using the VALUE or FORMAT function to convert one of the values.

The error is originating from ID being text and Amount being an Integer. I don't want to change the data type for the variable as it may affect other calculations I have in my data model. How then can I convert either variables (ID and Amount) to text or integer or viceversa?