I gave up. I've used Zen-Cart a couple times in the past and was never really happy with the ability to get shipping to work right, but I was mostly able to muddle through. I do actually sell internationally, but handling international is a bit of a tough pull using the cart. My latest site does sell some items which can add up in weight making international shipping a bit more problematic. It was was easier to just tell international customers their orders would be handled manually only.
One ACTUAL SHIPPING METHOD. I ship using only USPS Priority Mail in the US and to most other countries, but to some countries USPS will only insure Express... There are lots of little things regarding value of shipment, licensing, weight, etc. Something that was more work than it was worth to try and do with Zen Cart.
After my experience here in this forum I decided to try a couple other cart options. Most I tried had similar issues with shipping, but I was able muddle thru some solutions and get the shipping to work with one. I was even able to implement a "shipping will be invoiced separately" solution that works for customers in countries I have shipped to before and know will have minimal issues. This allows those customers to go thru a regular checkout.
While not the solution I hoped for it works using a weight and gross cart total solution by country.
I had tried Zen-Cart for this solution because I had used it before, but it turns out it was easier to use another cart. I had a bit of a learning curve with the new cart, but I was able to implement everything without any personal help. Just what was hard documented on-line. I choose my other carts to try, by looking at the user ratings from Softaculous users. I picked a short list of carts that users rated higher than Zen-Cart and started trying them.