How to summerize tfgld106.amth(1) field?

In Easy SQL you can use the "sum" Function, but not for repeating fields.
At least getting an error when trying.

When the sum Function is used for the amount field it looks like this:
sum(tfgld106.amnt):float0,
How do I use the sum Function for the home currency amount?
Please provide example if possible.

Thanks in advance
Eric