Here is my economic proof for a spherical earth...
The airlines count every penny! They are about economy to the fullest. They do not waste money.
Well, here is the test:
Put a flat map on table. Get some string. First, draw a straight line - using a ruler - from Seattle, Washington to Hannover, Germany. Cut a piece of string that length. Second, trace the path that airlines fly when they fly non-stop from Seattle to Hannover (you can see it on Flight Aware). You will notice that the path takes you over northern Canada, over Ireland, over London, en route to central Germany. Cut a piece of string that traces that path.
On the flat map - the "direct line" string is the shortest string. If the earth were indeed flat - that would be the route the airlines would take for sure. They are not into wasting money on anything. They would not fly a longer route to be part of a round earth conspiracy.
But, that is not the shortest route. If you take a globe - and do the same test - you will find that the shortest route is the polar route. The only reason this is true is because the earth was created by God as sphere.
I know Christian airline pilots. Men who love the word of God. One, in particular retired pilot who flew for Delta Airlines speaks in terms of the shorter nautical mile difference in flying - due to the earth's shape. It is a no-brainer. It is not a conspiracy that airlines want to fly the shortest routes possible.
I hope this humble submission is helpful in your thinking.