Ok -- not sure if this is the entire solution -- but I can provide the following lead...
We use xpsshipper.com -- which is a FREE service that gets paid from your use of USPS (but you can also plug in your FEDEX and UPS account numbers and it will do pass through charges to those accounts -- no surcharges).
It does NOT integrate with SQ. We discovered it when we were exploring solutions that work with Shopify (which we are still begrudingly using for our website). Shopify sucks --except everything else seems to suck more-- and it does NOT directly connect to SQ so we use it as what I refer to as a "brochure" site (or non-transactional).
Anyway -- we use the backend of our shopify site to do a form of memoing and invoicing for our theatrical clients -- and it works. We discovered xpsshipper.com from a FEDEX tech lead. We a big fans of HOLD at LOCATION -- and most of the shipping integrators don't offer that -- NOT shipstation (which is also expensive) -- not SHIPPO, not most of them. Anyway -- XPS OFFERS Return Labels from USPS that do NOT CHARGE unless USED -- which is RARE.
As I said -- it does NOT integrate with SQUARE -- although I have asked them multiple times. That said -- it consolidates all my carriers into one interface, provides comparitive pricing for services and does HAL. The only thing that is annoying is that it does NOT provide the comparison pricing for what retail costs would be for the same services -- so we still have to have a FEDEX window open to check what the client's cost for shipping is vs our cost.
Hope this helps.
