It's started again!
The same problem has occurred without any amendments to the system.
So I re-traced the steps as before including re-setting the API codes via PayPal, but not working still.
Are there any other steps that can be taken?
This was supposed to be straightforward and easy to integrate but I'vr found it anything but....and I have four more clients to setup too!
Is it possible that a FULL and comprehensive instruction sheet could be produced, because there are nmany steps missing from the one provided - just like the removal of USD $ and replacing with GBP £ - I found loads!