Looks at your first screenshot, you are concatenating cuerreny symbole (a text) with Amount (which is number) in a single expression by using And sign(&)
You can try two things.
1) fix that expression, by only specifying the amount, something like =Fields!LineAmount.Value and then let the formatting work. Basically separate the currency symbol(which is text), by putting it into a new cell/column and keep only the Amount field (if you want the system to apply formatting on it)
Or
2) slightly modify your expression in one of the few way, for example:
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