You will need a credit-based account.
Other accounts, such as Pay As You Go, will not allow you access to expressLink which you need in integrating your account with Shiptheory. It is best to check with your Account Manager if you're not sure what type of account you're using.
Once you're sure that you have the correct type of account, you can start setting things up:
Connecting your Parcelforce account to Shiptheory
If you have any queries or issues with this, please get in contact with support and we'll be happy to help!