Minecraft 1.15 Iron Farm not working?

Hi. I play Minecraft Survival on a server. I tried to build an iron farm. There are 6 villagers, all cartographers. They have access to beds and are chased away by the zombie all the time. Why don't iron golems spawn and what can I do to spawn them?

You can't see the zombie permanently.

I would recommend you to remove a design from YouTube, they are 100%.

I use this one and it works wonderfully. He also explains a little bit the mechanics behind such a farm.

I recreated the design of Ioser100 … It has a clock that pushes the zombie up with a pistol. Then the villagers are no longer stressed, but still don't spawn any golem.

Are you sure the Golem doesn't just spawn somewhere outside? E.g. Over the farm?

Unfortunately yes… I have the farm underground and there's no cave nearby and wherever there's space for a golem there's none