When paying to promote item (ie make premium, highlight, republish) using Bank transfer, it can't redirect to  cart instead it shows checksum failed

Is there possibilty to redirect also promote to cart? After clicking payment method

That usually happen if you try to alter url parameters

But this screen shot is from osclasspoint website pay plugin ,it shows the same "checksum fail" even when I install the plugin without altering anything it's same problem.


Then payment for e-commerce using bank transfer it's fine it works
For the case of promotion it doesn't seem to work 

Please provide step by step how to reproduce

1. Login as admin on
https://osclasspoint.com/osclass-plugins/payments-and-shopping/osclass-pay-payment-plugin-i46

2. Go to the frontend ,click on any item ,
3.On the promote section click process promotion

4. Click pay Bank transfer method
5. Next page will show checksum fail


I need solution to this

Thank you, fixed in 3.5.7

Thank you