...
It is very likely we will build a "public" API layer in the future with something like GraphQL. The reason is that this Rest REST API is pretty low level with a flat JSON structure. This means you will have to make a lot of individual API calls to get gather all the data that you need.
We envision a more public-friendly API in the future that allows external developers to better fetch data in a single request.
...
You can download the entire Swagger API definition by right-clicking the link below Api Documentation (near the top of the screen) and using your browser's "Save As" feature. The link should look like https://yourflexsite.flexrentalsolutions.com/f5/api/api-docs.
...
You can browse the cutting edge API's from Flex Dev here: https://flex5dev.flexrentalsolutions.com/f5/swagger-ui.html
First, let's get an Auth Authentication Token by going to the above URL, then click Authentication and Try It Out. Replace the Example Value information (username/password/source) with that which you receive in response to sending the signed terms & conditions document.
...
Writing Your Own Code
When you write your code against the API, the process will be similar. You'll have to post to the auth authentication endpoint to get a token and then send it down in the X-Auth-Token header for ALL requests.
If you're token is close to expiring the server will kick out a refresh token in the X-Auth-Token-Refreshed header. Our app just sniffs for the refresh token on each request, and if it finds one, it replaces the current one and starts sending the new one.
Good luck!