Same issue here. Going to mark this as a major issue because it blocks the actual submission.

Let me know if I'm wrong and if it gets solved someday :)

Why not define two or more decimal values and include it in the format?

The kata could include the following, as parameters of the function:

• precision, right now it would be 0 as you don't have decimal values
• decimal separator
• thousand separator

example prototype: def to_currency(price, precision=0, decimal_sep=".", thousand_sep=",")

results:
to_currency(1234, 0, ".", ",") => 1,234
to_currency(123456, 2, ".", ",") => 1,234.56
to_currency(1234, 3, ",", ".") => 1,123