How do I pay extra postage on label I have generated

[hapet-7222]

I accidentally bought wrong size postage label. How can I pay the extra now I have already generated it 

[arkwebus]

You "can" simply pay the extra at a post office though whether you can persuade them of that is a different matter!  The "proper way" is presumably to cancel the label for a refund and buy another at the correct price. 

@hapet-7222