Hey ,
Thanks for your assistance 
We do realise a lot’s been changed since 4.5 but our project is complete and we didn’t want to take chances on upgrading our version since all our development was done in 4.5.1
Having said that, we’ve used the ‘Make In-App Purchase’ blueprint method and also entered the Product Identifier properly in it. But still it gives a failure message each time. Went through a few posts online and tried to implement the IOSEngine.ini method but yet no success.