Problem with post codes

Hi
i use table rate plugin for my litle woocommerce
but i have a problem with orders from switzerland and spain for example.

in fact customers have to put “CH-” before their post code from switzerland, if they don’t add this it doesn’t work

same for spain, they have to put S- before post codes

my customers don’t know about this so they think they can’t order on the site because it doesn’t work for their ” normal” postcode without the letters

what shall i do ??

thanks

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