Further to our conversation, we understand that ["that" is not required, but I prefer it here] the existing certificate will be expired expire on July 31. Please advise the next audit perform date for us to the customer, becausewe are concern if the audit is not pass which will be affected for the shipment. I'm not sure I understand what you're trying to say in the second sentence (especially the second part of it, and the word "which").
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