MS Excel HYPERLINK() function with dynamic link_location does not work - why?

Question

I am trying to include the spreadsheet's own filename in an e-mail body dynamically created with the following formula including a VBA Module (?) function:

=HYPERLINK("mailto:"&"address"&"?subject="&B7&"&body="&B7&FullName(); "E-Mail")

The function is

Function FullName() As String
    FullName = ThisWorkbook.FullName()
End Function

in a "module" of the document (I don't have a clue about VBA: ALT+F11, Insert Module. Apparently this is also called user defined function (UDF)).

The function works on its own in a cell, the HYPERLINK formula works without adding to its link_location the function, but together (as above), it evaluates to

#NAME?

Links:

• Office docs: HYPERLINK function
• possibly related, but somewhat reverse problem: VBA to open Excel hyperlink does not work when hyperlink generated with a formula
• Hyperlink custom link_location formula is not dynamic
• Very similar problem: Creating a custom hyperlink function in excel

Answer 1

Follow this answer from the latter link in the question (do not use HYPERLINK formula, instead a function changes the manually created link in the cell).