TPPDF Swift: unable to add table to footer

Question

let footerTable = PDFTable(rows: 3, columns: 3)
    for i in 0...2{
        for j in 0...2{
            footerTable[i,j].content = try? PDFTableContent(content: "123123123")
        }
    }
    document.add(.footerCenter, table: footerTable)

I expected to get a table at the bottom of the page, but...

While: layout.margin.bottom = 0//(or other >0) document.add(.footerCenter, table: footerTable) => get nothing

While: layout.margin.bottom = -10//(or other <0) document.add(.footerCenter, table: footerTable) => footerTable at the next page