The best way to import multiple contacts at once is via the .csv import.

To import contacts using a .csv file, follow these steps:

1. Prepare your .csv file with the contact information in the correct format.
2. Go to the contacts section in the application.
3. Look for the import option and click on it.
4. Select the .csv file from your computer and upload it.
5. Click on the import button to start the import process.
6. Wait for the import to complete and verify that all contacts were imported successfully.

Format of the .csv

The easiest way to get the correct format, together with all the existing custom fields is to manually have added at leas one contact. And do an export.

The exported .csv will be in the format you need to do the import.