Zoho Projects API fails to update integrated field

Zoho Projects API fails to update integrated field

I would like to update via API a Projects' project custom field, which is an integrated_field with Zoho CRM Accounts module.

I identified the custom field identifier via the GET custom fields info api call, as described here. The custom field has id "UDF_TEXT1".

At that point, I performed an update query with a key-value pair that contained ("UDF_TEXT1", ID). I cannot find which ID I must use for the query to work. (I am able to update other custom fields e.g. a numeric field or a multiple choice field, but not the UDF_TEXT1 field)
I have already taken a look at the only Community portal related question, which does not specify how to retrieve the so-called crmContactId

I have tried the following IDs:
- ID returned by the Zoho CRM api
- Account ID displayed on the export CSV table obtained from exporting all CRM Accounts. This is the same as the Zoho CRM api, with a prepended "zcrm_"
- Account name as string

It is important to note that the API actually works. In fact, if I set the ID to the empty string "", the current Account associated with the project gets removed and the custom field shows "" as value.
The bottom line problem is finding which ID I should feed for the operation to work.

I would be very grateful if you can provide a response by today, since I need to present a dashboard from over 200 imported projects tomorrow and updating all account fields manually would be a big time sink.