V12 - Customize Sales Invoice Form

Hello. I am trying to add a custom field to sales invoice form. I am able to insert the field where I want to - but when I hit update - it does not save changes. I suspect that in V12 changes are not allowed to core doctypes?

I then created a custom field (under customization) - and selected point of insertion from drop down. Able to save the custom field. But does not show up on new sales invoice.

Will appreciate any guidance on how to add custom field to core doctype. Thanks.

Use “Customize Form” option to add custom fields and you should be able to add fields. If it does not show up immediately, try to “reload” the document.