UPDATE: If this happens to you, you can remove the API keys and Lasso will still work like normal. Lasso doesn't rely on the Amazon API anymore.
So you added your Amazon API details into Lasso and get one of the following messages:
"Error: You have no more Amazon Associates API credits."
"The request was denied due to request throttling."
This is because you haven't earned enough revenue with your Amazon Associates account.
According to Amazon, they implemented API usage limit on January 2019. They say, "each Amazon Associate account is calculated based on revenue performance attributed to calls (also called requests) to the Product Advertising API (PA API) during your account’s latest 30-day trailing period."
You're allowed an initial usage limit up to a maximum of 1 request per second and a cumulative daily maximum of 8640 requests per day for the first 30-day period after your account has been approved.
Following that, your API usage limit will solely be based on your shipped item revenue.
"Your account will earn a usage limit of 1 TPD (requests per day) for every 5 cents or 1 TPS (requests per second) (up to a maximum of 10 TPS) for every $4320 of shipped item revenue generated via the use of Product Advertising API for shipments in the previous 30-day period."
NOTE: Your account will lose access to Product Advertising API if it has not generated referring sales for a consecutive 30-day period.
For some context, this is a snippet from Amazon's documentation along with the source link: https://webservices.amazon.com/paapi5/documentation/troubleshooting/api-rates.html
NOTE: If you have just signed up for the Product Advertising API, allow for 24 to 48 hours for Amazon to start allowing your account to make API requests. If you believe you should have API credits, you can double-check that your API keys work here: https://webservices.amazon.com/paapi5/scratchpad/index.html. Or contact Amazon and ask them to check.