The customer fields the app uses most often are:

1. Company or customer name - shown on invoices and quotes
2. Email address - used when you send documents by email
3. Address fields - reused on document layouts that include address details
4. VAT number - shown on documents when that field is filled in
5. IBAN and payment terms - reused where billing defaults need them
6. Contact person and phone number - kept on the customer profile for reference

Complete the fields you want the app to reuse on new invoices, quotes, and send flows.