Complex sentence: However, Horvatinčić is forbidden to demolish Vidrić's home or build any part of the project until he obtains a building-location license, which requires him to prove he can build a walkway between Gundulićeva Street and Cvjetni Square.
Split into simpler sentences: However, Horvatinčić is still not allowed to proceed with the demolition of Vidrić's home, nor build any part of the project until he obtains a building location license. The license requires him to prove he can build a hallway between Gundulićeva Street and Cvjetni Square.