Amazon error code 99300 usually indicates an error or problem in the Amazon system, which may be caused by system failure, network problems or other technical problems. If you encounter error code 99300 when using the Amazon platform, you can try the following methods to deal with it:

1. Refresh the page: First, try refreshing the page and reloading the Amazon page to see if it can solve the problem. Sometimes, the error may be just a temporary problem and refreshing the page can solve it.

2. Clear cache and cookies: Clear your browser cache and cookies to make sure you are accessing the latest Amazon page. Sometimes, old cache and cookies may cause errors.

3. Change browsers or devices: If you encounter an error when using a specific browser or device, try using a different browser or device to access Amazon to see if it can solve the problem. Sometimes, different browsers or devices may have different compatibility issues.

4. Check network connection: Make sure your network connection is stable and there is no restriction or blocking of Amazon's network access. You can try to use other websites to check whether your network connection is working properly.

5. Contact Amazon Customer Service: If the above methods do not solve the problem, it is recommended that you contact Amazon's customer service team to report the error code 99300 you encountered and seek their help and guidance. They can further investigate and solve the problem.

Please note that Amazon error code 99300 may be caused by a temporary problem and may resolve itself after a period of time. However, if the problem persists, it is recommended that you contact Amazon customer service in time to get a more accurate and personalized solution.