If your project has Altegio integration, the process of creating a mailing list is done through the "Client Database" section in Altegio.
When you go to this section, you need to click on the "Excel Operations" button and select the "Download as Excel" action:
The uploaded table can include many different columns, but you only need to leave two of them - Phone and Name. If you leave extra columns, the customer numbers may not be correctly identified and the mailing will not be possible.
Example of a correct mailing list:
If you are not using Altegio integration, the mailing list is still created according to the same principle - it is important to have two columns, Phone and Name.