My sub form/page is not editable

Hi
Before migration sub-page was working fine, with minor customization and it is a copy of the Standard sales invoice but a completely new object itself.

Subform is not editable. it is going grey.

Does anyone
help me, please.

my code in AL is
page 50002 "POS- Sales Invoice Sub"
{
AutoSplitKey = true;
Caption = 'Lines';
DelayedInsert = true;
LinksAllowed = false;
MultipleNewLines = true;
PageType = ListPart;
Editable = true;
SourceTable = "Sales Line";
SourceTableView = WHERE("Document Type" = FILTER(Invoice));