Hi siroussamsami,
Thank you for contacting the Microsoft Community.
I understand that you want to extend the validity of your voucher for you to be able to take your PL-300 exam. Let me provide further information on this.
Upon checking, I have found the you have a previous thread with the same issue regarding your voucher expiration date as it depends on the terms and conditions of the voucher provider.
Should you need further clarification, please let me know.
If this solves your problem, please indicate “Yes” to the question and the thread will automatically be closed and locked. In case we do not receive a response, the thread will be closed and locked after one business day. Please be advised that after the case is locked, we will no longer be able to respond, even through Private Messages. If the resolution provided did not resolve the issue, please post a new question.