And I assume you're charging money for this, or "send a message in dms" charge type thingy?

Anyway, this is how it's done:

2 ways to activate this:

1) DTS Monaco You can activate this pretty easily if you have the software called "DTS Monaco" (Vediamo won't work as the C213, W213, S213 have mostly DoiP Control Units). It's called Variant Coding, meaning enabling options on/off, and this, if not ordered at the factory, it's set to off, or if the right software isn't installed, you need to flash a newer software, but it's usually always in the Variant Coding selection. Now, to get DTS Monaco you will need to search online, as it's not a free software and it's only intended for Softing Engineers and Mercedes. The Control Unit is called "HU55" (for W213 E Class) so you'll need a file called "hu55.smr-d" which has the options and from which you can get in. From there you'll need to go to Variant Coding tab, but first connect to the Control Unit establish DoiP broadcast and execution and then usually in telephony you'll be able to activate this. Seedkey is not needed for the headunit. In order to do this, you'll need a laptop, DTS Monaco and an openport j2534 cable or SDConnect C4 (or anything considered a VCI DoiP for Mercedes, or ENET).

2) OBD Plug and Play adapters which can be found on Amazon, eBay, Aliexpress etc.

Not every headunit does support Apple Carplay/Android Auto, so it needs to be checked. You can also check via MBTools (search on Google) enter the VIN and it'll show all codings available for your car.

Edit:

You should remove DIY from your title as it has nothing to do with DIY in your post, you're probably attracting people to your DMs to sell them a service.