If you are using Iways Paypal Plus, there are 2 options for proceeding
1) Iways PP+ notes on their website that their module version 1.8.2 has limited integration with onestepcheckout.com module. This has not been tested by us, however it is being used by some clients.
2) We have created and tested the following integration :
* Iways Paypal Plus 1.5.1
* One Step Checkout 4.5.5
* integration PATCH
Please contact firstname.lastname@example.org if you intend to use our integration PP+1.5.1, One Step Checkout 4.5.5, patch and we will send the packages to you.