Hello,
Please go To Sales and Marketing >> Inquiries and reports >> Order posting >> Sales order confirmation

Filter by the sales order you want to delete

Check if there is a record for which job status is waiting or executing
If you found the record, Select the row and press Alt+F9
System will prompt you to delete the record. >> hit yes

Try to delete the Sales order.
Please try the steps in Test environment
Thanks, Kaushik
This post is my own opinion and does not necessarily reflect the opinion or view of my company or Microsoft.
P.S:- Please mark the answer as verified if it heps you in resolving the issue.