If your issue is related to this thread, I think the simplest way is to contact the app developers of https://apps.shopify.com/shipfy-delivery-customization?show_store_picker=1  or email them at sid@cirklestudio.co They have good customer support and...

My thoughts exactly when scrolling down

No problem. Shipfy help me out as well during setup.

 @Shopify was pretty good about 3 years ago, but now they have a lot of low level support that honestly AI could answer.  Anyways,We did not have a direct answer for our customers to use their own shipping account number. What we did as a work around...

I would also like to know if this is possible.