This error isn't related to the delivery address but rather the shipping location, DPD require a name for the location where they collect your shipments.
You can add this on the shipping location page which can be accessed in the advanced options in the user drop-down menu
From here you want to enter the first and last name for the contact name of your shipping location and click 'save'.
Now any shipments that come into Shiptheory will not receive the 'ContactName is required' error, if you have any shipments that have already failed because of this error, you will want to select 'retry' on the shipments which will work as a refresh for the shipments and should book the shipments in correctly.
If this doesn't work or you need any help, just let us know by getting in contact with our support team.