The initial investment is locked up until the end of the maturity date of the tokenized security.
There are three cases in which you can get back your initial investment:
When the security you invested in reaches its maturity date (typically 10 years from issuance)
If the Issuer (German Estate Group GmbH) decides to sell the underlying asset before maturity date
If you are successful in selling your Pieces on the Secondary Market (How can I sell my investment?)