Using API To Ship Confirm Delivery Errors:There is an error generating/validating the sequence numb

Hi I am using   shipping API It is giving some errors
Warning: Some deliveries selected for Ship Confirm have errors or warnings.Error: There is an error generating/validating  the sequence number. Please check the assignments are defined and are valid.
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Warning: Pack Slip information could not be automatically created for delivery 965613.
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Warning: 1 deliveries will be marked as In-Transit/Closed.

It is Making Ship confirm But Giving these warning.

Script That I am using is it.
How can I resolve these errors

declare
 x_msg_count number;
     x_return_status varchar2(1);
     x_msg_data  varchar2(1000);
     l_trip_id number;