Excel VBA Xlookup Function - #VALUE! error when using variable

Question

When I specify a cell for the variable, it returns the value I would expect as per below.

but when I change arg3 to be defined by a function, it starts to return a #VALUE! error.

I don't understand the reason for this. The line of code which the variable is calculated from definited works as shown below.

Can somebody please help me find and fix the issue.

Thanks

Answer 1

Issue fixed...

The variable has been defined as Double and this fixed the error.