How can I find when clients signed up to the store?

I am looking at Master Data client report and I cannot see when a client first signed up. I see the following columns: createdIn but the dates don’t seem to be the data I am looking for. In most cases it is nearly the same as lastInteractionIn.
I am trying to match the master data information to google analytics /registration page.
Thanks for your help.

You should be able to get that information in the createdIn field of the Master Data record for that customer, using the Get Document endpoint of Master Data V1.

I just tested running this cURL request on a test account to check my own user:

curl --location --request GET 'https://{{accountName}}{{document_id}}?_fields=createdIn' \
--header 'Content-Type: application/json' \
--header 'Accept: application/vnd.vtex.ds.v10+json' \
--header 'x-vtex-api-appKey: {{x-vtex-api-appKey}}' \
--header 'x-vtex-api-appToken: {{x-vtex-api-appToken}}'

And this is what it returned:

    "createdIn": "2019-12-03T21:59:22.0916546Z"

Which is compatible with the date/time I signed up to the store. You can also specify _fields=_all to get the full data structure for the customer, if needed.

Could you elaborate further on why you believe that is not what you are looking for?