
Here is what happens when you reach the contact limit on your current subscription plan:
Import contacts via sync
If you've enabled the Auto-upgrade option under Settings, Zoho Campaigns automatically upgrades your subscription, allowing you to import contacts via a sync you've created. The upgrade will be based on the number of contacts you are trying to import.
In case you haven’t enabled the Auto-upgrade option under Settings, the sync will stop, and no additional contacts will be imported to Zoho Campaigns upon reaching the contact limit.
Import contacts via files
If you try to import contacts via .csv, .xls, and .xslsx files after the plan limit is reached, you'll be asked for consent each time you try to import the contact. If you give your consent, we will upgrade your plan before importing the contacts.

Note:
The charges will be added up to your next billing cycle.
Switch to pay-as-you-go plan to choose your email credits as per your requirement. Pay-as-you-go allows unlimited contacts.
Log into Zoho Campaigns.
Click Settings on the top-right corner of the screen.
Select Subscription under General. You will see your current plan.
Click the Upgrade button in the top-right corner. You will be redirected to Zoho's payments page.
Click the Change Plan.
Select the option to switch to Email-based.
Choose the plan options you want.
Click Upgrade Now.
Switch to pay-as-you-go plan to choose your email credits as per your requirement. Pay-as-you-go allows unlimited contacts.
Log into Zoho Campaigns.
Click Settings on the top-right corner of the screen.
Select Subscription under General. You will see your current plan.
Click the Upgrade button in the top-right corner where you can see your current plan.
Click the Cancel my subscription link at the bottom of the page.
Your plan will automatically be changed to a pay-as-you-go plan with zero email credits.
Click Buy Credits.
Choose an email credit plan from the list.
Switch to email-based plan to purchase a certain number of emails you can send. You can have half as many contacts as the number of emails you purchase. All features are available, except for autoresponders and the send email option in workflows.
Log into Zoho Campaigns.
Click Settings on the top-right corner of the screen.
Select Subscription under General. You will see your current plan.
The Upgrade button in the top-right corner. You will be redirected to Zoho's payments page.
Click Change Plan under Manage Subscription.
Select the option to switch to email-based and choose the plan options you want.
Click Change.

You can download the invoice using this link.
Before choosing a plan for your organization, you need to know the difference between the plans. Difference between pay-as-you-go plan and the email-based plan are,
The pay-as-you-go plan allows unlimited contacts, while the email-based plan only allows half as many contacts as the number of emails purchased.
The email-based plan is on a recurring payment cycle, meaning that the payment is taken automatically each cycle. The pay-as-you-go plan is not on a recurring cycle.
Purchasing or subscribing to a plan is a one-step process with our payments team if your credit card details are saved. Follow these steps to edit your credit card details on the Payments store.
Log into Zoho Campaigns.
Log in to Zoho Campaigns.
Click Settings, then select Subscription. You will be redirected to Zoho's payments page. From here, you can easily view all the products you have purchased from Zoho, and manage them on a single platform.
Select a model you prefer—either Subscription plan or Pay-as-you-use.
Choose your plan from the list, then click Upgrade.
Check the plan's price, then review your order and make the payment. A summary of your plan and payment will be displayed.
In case you cannot view the add-on on your Zoho Campaigns application post the approval, please contact support for assistance.


Note: If you've added less than 2000 contacts, then you can send 6000 emails.
The paid subscription plans are:
Professional plan: This plan is based on the number of contacts in your account. Purchase the plan for a specific number of contacts, then send those contacts unlimited emails, set autoresponders, and use workflows.
Standard plan: This plan is also based on the number of contacts in your account. The major difference between this plan and the professional plan is that some features like autoresponders, dynamic content, and email polls are not available in this plan.
To disable the auto upgrade option for your subscription plans of Zoho Campaigns:
Click the Settings icon.
Click Subscription under General.
Toggle the Auto topup to disable it.

Note
If you disable the auto-upgrade option, you won't be allowed to add new contacts. This is likely to affect workflows, your attempts to add new contacts and set up syncs.