Users of Certify'em are subject to usage quotas (limits) which affect how many responses and certificates Certify'em can process per day. These limits are set by Google, not Certify'em, and depend on the type of Google account you have. These quotas do not change or increase if you purchase a plan from Certify'em.
Please review the sections below to understand these limits, and whether or not Certify'em will meet your needs.
Daily Email Quota
If you're using a regular Gmail account, Add-ons like Certify'em can send only up to 100 emails (certificates) per day*. If you're using a paid Google Workspace (G Suite) account (read more about Google Workspace here), Certify'em can send up to 1,500 emails (certificates) per user per day*. These limits are imposed by Google, and not by Certify'em. Note that if you choose to send emails for exam attempts (an email is sent even when exam-takers don't pass), then those emails also count towards this limit. Exceeding this daily quota will affect the ability of Certify'em to send certificates until it is reset by Google (every ~24 hours).
* Assumes no other installed Add-ons that are also sharing this daily email quota. The higher Google Workspace limit of 1,500 can take several billing cycles to kick in for new customers.
Daily Server Quotas
Users of Add-ons like Certify'em can be subject to other daily quotas from Google too. These quotas are imposed by Google, and not by Certify'em. These are related to factors like total processing time per day, total database accesses per day, usage of Google Drive services, etc. Exceeding these quotas will also affect the ability of Certify'em to process responses and send certificates until they are reset by Google (every ~24 hours).
What Happens If I Exceed a Quota?
When you surpass a daily quota, Certify'em can no longer process Google Form responses and send emails to exam-takers. To avoid the confusion this may cause, Certify'em will try to automatically turn OFF certification and disable access to your exam if it detects you've exceeded any of these daily quotas. This is to ensure that exam-takers can always receive a certificate if they take your exam. Users visiting your exam will see a message like "This form is no longer accepting responses". Additionally, you will not be able to resend certificates manually until the quotas have reset.
Quotas are reset by Google approximately every 24 hours. After turning certification OFF in your exam, Certify'em will check back every hour until these quotas from Google have reset, at which point it will try to turn certification ON and and reenable exam access. You will not be notified again by email when certification is turned back ON.
Even once your daily quotas have been restored, any Google Form responses made while quotas were exceeded will not be automatically reprocessed by Certify'em. You will instead need to reprocess these using the Resend Certificates functionality of Certify'em.
Can My Daily Quotas Be Increased?
Daily quotas are set for Add-ons by Google, not Certify'em, so unfortunately they cannot be increased.
If you need to send more certificates each day than you can now, here are a few options for you to consider:
Share via Drive: Instead of emailing certificates, consider the option to share via Google Drive (see advanced options). This works because the email notifications are sent by Google Drive, and not Certify'em. Exam-takers will also be able to find their certificates in the "Shared with me" section of their Google Drive. Note though that:
Google Drive has its own quotas (see Daily Server Quotas above), and while you may be able to share more certificates with this method compared to email, you may still reach a daily limit.
Recipients will need a Google account (i.e. Google Workspace or @gmail.com) to be able to print or download the certificate. Else they will only be able to view the file and will have to take a screenshot.
Use multiple accounts: If you have more than one exam, you could consider setting up a dedicated @gmail.com account for each exam. This does not change the daily quota set by Google, but would allow each exam (account) to take full advantage of it.
Setup a Google Workspace account: If you are using personal Gmail, you are limited to 100 emails/day by Google when using Add-ons like Certify'em. In comparison, Workspace accounts can send up to 1500 emails/day. Note that:
Google Workspace is not free in most circumstances.
Plan on setting aside a few hours to purchase and setup Google Workspace.
The higher per day email limits for Google Workspace accounts won't take effect until (1) your Workspace domain has cumulatively paid Google at least USD $100 (or equivalent), and (2) at least 60 days have passed since reaching that payment threshold. You will need to plan for this time, and/or pay the $100 USD (or equivalent) early. See this article for more on paying early.
Even when setup properly, for new Google Workspace domains it can take at least 60 days before Google stops treating emails sent by Add-ons (like Certify'em) with more strict SPAM filters. Ergo, emails with certificates send outside of your Google Workspace domain may bounce back during this time.
You should read this article carefully for a more detailed discussion of using Google Workspace.