FLTP_TO_DEC conversion in CDS extension view

Hi,

I am currently working on extending a standard view, which involves calculations and conversions of numbers. I noticed that I am receiving an error: "The current expression is not supported in the selection list", but I am uncertain as to why this expression would not work. Is this a limitation within CDS Extension views?

When reading through the documentation I am following the correct syntax, the only difference I can see is that this is a CDS Extension. However, I cannot find any information if this function is not available. Would you perhaps know why this expression is not available in a CDS Extension View?

Best regards,

Hendrik