To participate in Amazon Flex, it is essential to use a vehicle that meets specific requirements. The vehicle must be a mid-size car or larger, with a seating capacity of at least five passengers. This means that a three-door vehicle, which typically has limited seating and space, would not qualify for Amazon Flex deliveries. The policy is in place to ensure that drivers can safely transport packages and have enough room for the deliveries. However, there are exceptions for certain types of vehicles, such as vans or enclosed bed pickup trucks, which are allowed because they provide better protection for parcels against adverse weather conditions. Therefore, if you own a three-door vehicle, you will need to consider alternative options that comply with Amazon Flex's vehicle requirements to be eligible for the delivery program.