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Contact custom fields in v2 size limit 50 or 255? and how to reference.

Regular Participant

Contact custom fields in v2 size limit 50 or 255? and how to reference.

We are developing an application using the API and the Java SDK.

We are trying to add custom fields to a contact and add the contact to a list and add the list to the account.

Prior testing of creating and adding contacts in a list and scheduling a new campaign for that list have all worked fine.  Nice API.

However, now we are attempting to add custom fields.  The documentation on-line says that the size limit to values of custom fields is 255 characters, which limit we are under.

But, when we execute the code we get a failure response as follows:

[{"error_key":"json.max.length.violation","error_message":"#/import_data/0/custom_fields/0/value: Value exceeds maximum length of 50."}]

Our values are, indeed over 50 chars, but under the 255 chars.  Is this a missed change? (We note that previously the limit was 50.)  Or is there something else wrong?


Also, the api and documentation suggest that there are now unlimited custom fields, and that they can have assigned names.  If so, what is the proper syntax for referencing a custom field named (e.g.) "My Custom Field 6"? Would that be "SUBSCRIBER.MYCUSTOMFIELD6"? Or something else.

Thank you for your assistance.

Regular Participant

Sorry, original post was by me, should have posted from this account.  Please reply to this message not the above. Thanks.

In our API, we currently only support 15 custom fields with a limit of 50 characters.  This is because not all of our customer base is on our new Contact Management platform (which it sounds like you are on) and doesn't have access to these additional features.  To maintain a consistent and predictable API experience, we are continuing to use the stricter limits of the older Contact Management platform until we have 100% of our customers migrated and can expose the new functionality and limits.


We recently have announced that we have migrated more than 500,000 of our more than 600,000 customers and that we are on track to finish migrating in the not too distant future.  Unfortunately, I can share more detailed information than that today but we are making great progress on finishing our migrations.  Once that happens, we will start to roll out new functionality, limits and features as quickly as we can.

Dave Berard
Senior Product Manager, Constant Contact
Occasional Participant

4 years later, the limit is still there in the api, but not the GUI. Any updates?


Thank you for reaching out to Constant Contact API Support.

We are working on a new V3 API version which will have named custom fields with the same character limits as our website UI. Our current goal as of right now is to have contacts endpoints ready for release by the end of Q3 or early Q4. Unfortunately I don't have a more specific date for you.

David B.
Tier II API Support Engineer

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