There can be a few reasons that your contacts are not syncing in campaigns from Zoho CRM.
No email id in the account of your customers :
The reason your contacts are not syncing with Campaigns is, there may not be any email address in the account itself. It has been observed many times that the email address is blank for accounts. While syncing the contacts into Campaigns from your CRM account, it rejects all those contacts automatically which doesn't have an email address in it.
While syncing the contacts in your campaigns account, you shall also consider the field 'Exclude email opt-out'. This field lets you import only active records and ignore the records which have opted out of Zoho CRM.
Sync issue while integrating Campaigns with CRM :
It is generally observed that while integrating Campaigns with the corresponding fields are not mapped correctly or there can be some issue while you try to sync the data. This causes the sync issue, hence while transferring data to campaigns from CRM the system is not able to pull out all the data.
This issue can simply be fixed by editing the field mapping and re-mapping them with the corresponding fields in order to sync the data between them. You should also check the data you are trying to pull has been correctly mapped with the CRM fields and modules.
Also, while syncing you have this option to 'Retrieve data' from CRM into Campaigns. This 'retrieve' option lets you sync the data from your CRM to your campaigns account. You have the option to choose between 'All data' and 'Data added after' a given date and time according to which you will be able to sync your data into Campaigns. So, if there are few new records and data was synced before the time it was added, those records won't be reflected after syncing. In those cases please check this Retrieve data.
Data security and privacy policy :
Zoho takes data privacy and security very seriously. We comply with all the data administration and protection law implemented across the world such as GDPR, HIPAA, etc.
Say if you have 1000 contacts in your CRM account and you want to sync that data to Campaigns, you may get less than 1000 records in your campaigns account. This is because of the various data security compliance.
Customer consent :
Many times customers unsubscribe to getting updates from company about any event, products, marketing emails or ads. This is also included in your Campaigns under 'Lawful basis for communication'.
Already an existing Contact :
In case there are duplicate records available in your CRM, while syncing the contacts all those duplicates will automatically get rejected in your campaigns account. Also, when a record exits from a custom or criteria-based view in CRM, it's not updated in Campaigns.
2. Why did I get a 'Hard Bounce' message in sales signal of my CRM account right after sending a campaign?
There can be various reasons for the 'Hard Bounce' message in your CRM account. It can be email address bounce, parameter failure or backend related issue.
You can get the reason for the hard bounce under the 'Bounces and Auto-replies' field in the 'Reports' tab of your campaigns account. Once you know the reason, it will be easier for you to troubleshoot that issue by contacting your email service provider or by zoho support team at crmsupport@zohocrm.com

3. Why is that my campaigns account shows, I have successfully integrated with CRM. However, when I check in my CRM account some error occurs?
While integrating Zoho campaigns with your CRM account some errors might have occurred during the integration itself, such as wrong field mapping, configuration-related issues or customization-related problems.
In most of the cases it can be troubleshooted simply by re-mapping the fields between the campaigns and CRM account. Identical fields (same data type) of CRM shall be mapped with identical fields of Campaigns. Such as the account name in CRM fields shall be linked with account name of campaigns fields. Also, proper configuration can fix these sort of problems.

If the problem persists even after re-evaluating the configuration. Delete the integration and try re-integrating it. However, re-integration is advisable only if neither of the above-mentioned tips help.
4. Why am I getting 'permission denied' error while trying to integrate campaigns with my CRM?
Check that you have the permission to 'add extensions' in your profile. In case, if you don't have proper permission to perform any integration, 'permission denied' error occurs.
Check with your system admin that you have the permission to integrate marketplace apps into your CRM account.
For a user having a standard profile, the privilege to access extensions will be denied by default. You need admin level permission or admin profile in order to access the marketplace extensions.

5. Why the layout for 'Zoho Campaigns' still exists though I have deleted the integration from my CRM?
While you delete something from your CRM, it remains in the 'Recycle Bin'. To delete something permanently, you need to delete it from the recycle bin as well.
Deleted items exist in your CRM till they have not been permanently deleted. So, if you don't need those deleted items anymore, the best practice is to delete them from your recycle bin as well.
Once you delete the layout from your recycle bin, it won't be reflected into your account anymore.
6. Why am I getting this error message of 'your org is already integrated' when trying to integrate Campaigns in my CRM account?
This error will occur when you try to integrate your CRM with Zoho Campaigns from the same account which has already been linked. It can be that you are trying to integrate campaigns into your CRM account from the same account which has already been integrated before.
In case you don't know or remember doing this, first check whether your CRM account has already been integrated and if so, try deleting that previous integration.
If your account has never been or is not already linked to Zoho Campaigns but you are getting the same error, please feel free to reach out to our CRM support team at crmsupport@zohocrm.com
7 . Why am I unable to view the image in campaigns record though I can preview it?
This type of issue arises when a user having different profile permission creates a record, while the user who is accessing it has a different profile permission. Say for example there are two default profiles in your CRM, Standard and Admin. These profiles differ in permission to access or perform different tasks and functions.
These types of issues can be fixed simply by enabling the permission for 'custom fields' under 'Roles and Privileges' in your Zoho Campaigns account for the given user or by simply giving Standard admin level access to that user.
8. Why am I unable to copy the customization field though I have deleted the campaigns integration?
To copy customization field from your CRM account you need to disable the integration between your CRM account and Zoho campaigns. Deleting the integration will unlink all the data between campaigns and your CRM account. All the sync will be deleted and you won't be able to sync any live data. Don't delete the integration or deactivate it. Just 'Disable' the integration, if you want to copy customization in your CRM account.

On the disable integration page, you get to choose between two options Deactivate and Disable. Always select disable to copy customization.
9. Why my Member status is not being updated in campaigns module of Zoho CRM?
Ensure whether the 'Update Campaign Member Status in CRM' is enabled in your campaigns record under 'advanced options'. If the status is disabled, your member status for users won't be updated to the campaigns module in Zoho CRM.