Did you mean to use "L_PAYMENTREQUEST_n_NUMBERm" ?
I don't think there is a PAYMENTREQUEST_0_NUMBER.
L_PAYMENTREQUEST_n_NUMBERm
(Optional) Item number. You can specify up to 10 payments, where n is a digit between 0 and 9, inclusive, and m specifies the list item within the payment. These parameters must be ordered sequentially beginning with 0 (for example L_PAYMENTREQUEST_n_NUMBER0, L_PAYMENTREQUEST_n_NUMBER1).
Character length and limitations: 127 single-byte characters.
This field is introduced in version 53.0. L_NUMBERn is deprecated since version 63.0. Use L_PAYMENTREQUEST_0_NUMBERm instead.