PQendcopy error in multithreading

Hi,
        I am trying to update multiple tables using the 'PQputline/PQendcopy' function. The code works fine if the tables are updated one after the other.
However, if there are multiple threads trying to copy data into different tables, the function fails. i.e. if one thread has started its copy operation and if some other thread also starts its copy operation (on different table), one of them fails.
Strangely, the PQputline function is successful for both the threads after the end delimiter is sent (\.).
What might be the reason for this PQendcopy failure? How do I get the exact error message after the failure?

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