Please provide more what issue you are facing in voucher numbering. Further you can set the voucher numbering by using these steps:
Step 1: Go to Administration and click on configuration.
Step 2: Choose the Voucher Series Configuration and select the voucher type of that you want to enable voucher numbering for, such as sales, sales return, etc.
Step 3: Then, select the voucher series and click on Voucher Numbering.
Step 4: Choose the Numbering Type as either Automatic or Manual.
Step 5: For automatic set the prefix, suffix, and Starting No. as per your needs and click on OK to save the settings.
Note: Take backup of your data before making any changes.