Actually, this might be a native speaker, but it's the sort of confusing language often found in legal documents, sometimes called 'legalese'. It seems to be saying that you have at least 30 days to pay after the invoice. I agree with Paul, to the extent that it's very annoying and confusing.

I'm native English speaker. The person who wrote this is not a native. It is probably Copy/Paste from a poor source. However, it seems to say that the payment is due within 30 days of the date of Invoice.

The clause you provided states that any payment under the agreement is not due until at least 30 days after the date of the invoice. Let's break it down for clarity: Date of Invoice: This is the date on which the invoice is issued by the party providing goods or services. "Not less than 30 days after the date of invoice": This phrase means that the payment due date will be a minimum of 30 days after the date of the invoice. In other words, the payer has at least 30 days to make the payment. So, to provide an example: If an invoice is issued on January 1, the payment would not be due until at least January 31 (30 days after the date of the invoice). The payment due date could be later than 30 days, depending on the terms of the agreement or invoice, but it must be at least 30 days after the invoice date. In summary, this clause ensures that the party receiving the invoice has a minimum of 30 days to make the payment, but the actual due date might be later, depending on the terms specified elsewhere in the agreement.

In real life I would try hard to ask the person who wrote the agreement. I can't tell for sure what it means. I think there's a possibility that the writer made a bad mistake and said "shall not be due" instead of "shall be due." I recently signed a contract for gutter repair and it contained several places where I asked them to make the wording clearer. It wasn't a tense negotiating situation. In every case they said "sure," and changed the phrase to be clearer. In a friendly situation, it is to everybody's benefit to be as clear as possible. Legal language is more like a computer program than everyday English. It isn't normal English. It really takes a lawyer to say what this means. As written, it SEEMS to me to be saying that the payer will be allowed 30 days or more to make the payments. The strange "not less than 30 days" might be a way of resolving some ambiguity about whether the exact 30th day is included. As written, this only makes sense if the person writing it is MAKING payments to you and wants to be sure they will be allowed 30 days.