If you experience technical difficulties downloading a Certificate of Completion from the IHI after finishing one of their Open School courses, you can provide a screenshot of any view in your IHI account that shows you have successfully completed the course.
As long as the screenshot indicates you have completed the course, your instructor should accept it.
Example:
Be sure to check back in your account to see if a certificate becomes available for you to download and save to your own computer. Certificates expire after one (1) year, which means that the IHI removes them from your account and you will no longer be able to access them.