how to check PO amount at run time and trigger error message ?

Hello Everyone !!

My requirement is to validate PO pricing amount with PR pricing amount. Please check the below image. As you can see that

Gross Price is 1,000.00 INR which is same as corresponding PR amount. But if it is not then i have to trigger an error message. So, please suggest me the BADI or EXIT which i should use to solve the problem.

with best regards,

Santanu Nayek