There are two ways to get AMS data into AHS. The easiest way is to allow AHS access to your AMS account (no need to share your password or anything creepy like that):
IMPORTANT: Each day At 4am and 4pm ET we request all of the reports from AMS. This is just a request but does not guarantee they will send it quickly. AMS puts the request in a queue. Then every half hour on the hour (i.e. 4:30, 5:30, 6:30...) we'll check if your report is available. If it's there we grab it for you. If not, we'll try again. Different countries' data will likely come in at different times.
NOTE: If you sign up today you might not see data until tomorrow. While data will not be up-to-the-minute, you no longer need to upload daily AMS data if you use the tool!
You can also manually upload your ads data:

STEP 1 – Make sure you’re on the main campaigns page and select the date you want to download.
NOTE: Amazon often updates the data multiple days later, so you should always go back a few days to make sure that you have the latest data. How many days is unknown, but we tend to look back 10 days.
NOTE: DO NOT use date ranges. Amazon does not split the data up over date ranges. You must upload only ONE day at a time. If you do a date range and upload it, you’ll just see a big spike for that day. If that happens, simply download the single day’s worth of data and then upload it again.
Make sure you’re looking at all campaigns, not just one campaign.

Also, be sure you are in the multi-country view so you can capture all ad spends across all countries. You can find this setting in the upper right corner of the screen. Click on the text “Sponsored ads – Author” to see your options.

Select the specific date you want to download. Select only ONE day. Date ranges are not supported because AMS reports over 2+ days don’t identify what spend happened on which day. Click the “Export” link and download to a place on your hard drive where you can easily find it.

STEP 3 – Upload your report to The Author Helper Suite
The key component here is that you want to make sure you select the right date for your report. This is only necessary for Amazon ads reports because–for reasons we can’t explain–Amazon does not put the date in their reports.
NOTE: The Author Helper Suite has no way of knowing if the date of the report is correct for the date you select. The good news is that if you accidentally select the wrong date you can now simply upload the report again using the right date! Just remember that you’ll also need to re-upload the report for the date you had accidentally selected.
Follow this image for details.
STEP 4 – Do sanity checks on the data
At certain intervals, you’ll want to check the data to make sure that Amazon hasn’t updated your daily spends. About 10 days into the month, take a day to fully look over the previous month’s data, for example.
Follow these images for details.