Issue Setting Up Shopify Shipping/Sendle

I want Sendle to show live rates at checkout for customers. It will only show if I select Sendle Unlimited. If I select Domestic or Satchel nothing shows at checkout. Sendle Unlimited rates are not accurate as they are for unlimited weights in an A4 size satchel. Customers can only get this rate even if the goods will not fit in the satchel. I have been going round in circles talking to Shopify and Sendle and still have no resolution. Can anyone help?