Versions:
carpetskyadditions-1.19.2-4.1.2.jar
fabric-api-0.62.0+1.19.2.jar
fabric-carpet-1.19.1-1.4.83+v220727.jar

I followed the instructions:

Multiplayer
The mod is only required server-side.

Create a Fabric Server
Download fabric-api
Download fabric-carpet
Download Carpet Sky Additions
Start the server to generate a template server.properties file
Shut down the server
Delete world folder the server created
Place fabric-carpet, fabric-api, and SkyBlock into /mods/
Open server.properties
Change level-type=minecraft:normal to level-type=carpetskyadditions:skyblock
Start the server
Run datapack enable "carpetskyadditions/skyblock" to enable the datapack

Also ran:
datapack enable "carpetskyadditions/skyblock_acacia"

Then player logs in for the first time.

Starter Island is still Oak Tree. Did I miss a step?

Much appreciated.

The problem is that the acacia datapack must be enabled before the world generates which isn't really easy to do on a server world.

I thought this may have been the case watching the server log as the mod spun up. Using the provided datapack was easiest for me as I have created my server in a docker container. (although I did spawn on top of the tree lol).

Thanks for the quick response!

You need to change level-type=carpetskyadditions:skyblock to level-type=carpetskyadditions:skyblock_acacia to spawn acacia tree instead oak

You need to change level-type=carpetskyadditions:skyblock to level-type=carpetskyadditions:skyblock_acacia to spawn acacia tree instead oak

This is not correct. This would just fall back to the default worldgen.

The problem is that the acacia datapack must be enabled before the world generates which isn't really easy to do on a server world.

I think the best option for acacia gen on a server is to generate the world in single player then copy the save to your server renaming it to "world".

I will update the docs to try to reflect this.

You could also download the datapack here and put it in your datapacks folder. Then delete the world folder and restart the server. This might be eaaier.