The WorldPay Express API documentation (page 19) says the limitation of LineItemCount is up to 998 for Visa and 98 for Mastercard.
But what about Amex?
This reference in the Express Interface Specification document is incorrect. The Express platform supports up to 50 Level III line items in a given transaction.
Also, at this time, Express does not support Level III commercial card processing on Amex. Only Visa and MasterCard are supported.
We'll work on updating the Express Interface Specification accordingly. In the meantime, I'm going to e-mail you our Express Level III Overview document, which provides more detailed and precise information.
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