If you are working Payments Pro UK and not Payflow specifically you should be using the PayPal API username, password, and signature for the transactions.
These are different than the Payflo credentials that you have entered in here now. You should be able to login to your PayPal account and obtain the Payments Pro API credentials. You will need an api username, api password, and signature. These will differ from your standard paypal username and password that you use to login with.