Hi Sreeram,
Thank you for reaching out to us. There are a couple of constraints that you should consider when using TrialService. The endDate can be updated to a different future endDate as long as it is not in the past or overlaps with any other running/scheduled trial, must be within the base campaign’s [startDate, endDate], and endDate must be later than startDate. If your endDate passes these requirements and you’re still running into issues, could you please send me your SOAP request and response logs so that I may look into this issue further? Please reply to me by clicking "Reply privately to Author".
Thank you,
Bryan, Google Ads API Team