generate a barcode to track item

I am currently working on a Web portal and I want to track my items going to different places.

Basically, my items have to go from our warehouse to let say "Client A" and then "Client A" have to send this item to "Lacation B".

I would like my Web portal to generate a bar code with "Client A" address and "Location B" address, and anytime the bar code is scanned by a delivery company, the Web portal will be updated.

All the items are more or less the same sizes and weight and the idea is to prepaid the cost of delivery within the bar code.

I am based in the UK and I am aware that Royal Mail has an API, my question is do you guys know if they are other API worth looking into it? Or would it be better to build are own?

Also we are planning to ship worldwide at a later stage, does that mean we would need to get an API for every country we want to ship to?

I don't have any experience on retail, looking forward to learn from this industry.

I hope that make sense, thanks in advance