The error message will tell you what the problem is - if it says it can't find a posting setup record then it's because you have not set it up, if it says a field cannot be blank then you need to populate it.
If you don't understand the error message then you need to tell us the actual message otherwise we can only be of limited help.
Answers
Please show error. Plobably you must enter a field which one is using while posting.
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If you don't understand the error message then you need to tell us the actual message otherwise we can only be of limited help.