Basta abrir
app/code/WebShopApps/MatrixRate/Model/ResourceModel/Carrier/Matrixrate.php
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$postcode = $request->getDestPostcode();
Logo abaixo adicionar
$postcode = str_replace(‘-‘,”,$postcode);
Créditos: https://www.vitaminaweb.com.br/atualizacao-da-planilha-de-frete-para-magento-matrix-rates/