I spent quite some time in their cost explorer, but I don't understand a lot. Most days I have some positive costs, which is probably my usage. Some days I have negative cost, that's probably when they transfer credits from the voucher. They do this every end of month, but also irregulary some days when I use particular services and/or have higher than usual service.
It appears to me that the negative balances are a sum of costs of several days and the credit from the voucher. As a simpliplifed example I might see +1, +1, +1, -6. So I "reverse engineer" this as I "spent" 1, 1, 1, 3 and on the 4th day they credited 6 from my voucher. Too bad the 3 is not visible, I need to dig it out myself. In reality I use several services and they seem to credit them on different days. So the reverse engineering is not really possible. At least not without a major effort.
I remember many years ago it was possible to download hourly (probably also daily) usage reports. I.e. is usage in hours, KB, requests etc. not in money. I don't find them at all anymore. Anybody knows whether they still exist?
Also to my surprise I was billed 135 SQS requests last month. Well, I wasn't billed, because 1,000,000 are free. But my point is that I don't even know what SQS is and I am sure I haven't used it directly. It appears to me that they are "billing" me for their implementation details, because they might use those SQSes internally. Is that how it works? So if basically not using the services at all causes 135 requests, how much would that be if I really run some production there?
All in all, very opaque. Thank you AWS for the voucher, but I am not impressed about the billing transparency.