The Google Ads API will reduce the maximum number of user_identifers for one set in UserData from 100,000 to 20. The change aims to have each set in UserData represent one user, according to the Google Developers blog.
UserData is used to download email addresses and store conversions. The Google Ads API team provides an example of correct and incorrect use of user_identifers sets in UserData.
There are two users (John Doe and Max Mustermann), each with two email addresses. It will be correct to create for each user one set of user_identifers with addresses.
The Google Ads API team clarifies that the same total amount of data can be sent in a single request, but each set of user_identifiers must represent one user.
Now, if the number of user_identifiers for one set exceeds the new limit of 20, the TOO_MANY_USER_IDENTIFIERS error will be generated.
This will be applied to the two Google Ads API methods that load the UserData:
NIX Solutions notes that the update will take effect on January 10, 2022.