Google Analytics (GA) account prefix is used when you are want to push data into multiple GA accounts. If you are tracking a page using more than one GA account, define an account prefix to specify the GA account you want to integrate with VWO. Based on the prefix, VWO pushes data into the respective GA account.
For example, consider that you are tracking a page with two or more Google Analytics accounts where main and rollup are the GA account prefixes defined inside the UA code.
If you want to push VWO data in Google Analytics account id: UA-XXXXX11-1, enter main in the Account Prefix field and 1 in the Custom Dimension field. If there is no prefix defined, leave the Account Prefix field blank.