Hi Ting,
Thank you for reaching out. The Internal error is usually temporary so if you retry after some time the issue might not exist any more. Another thing I would like to mention is that could you please upgrade your client library from v1 to v2 to have a better experience as in v2 some critical bugs have been fixed and that could be the cause of the issue. Please let me know if you have any further questions.
Thanks and regards,
Xiaoming, Google Ads API Team