following the spec hEX can supply 500ma while ac2 requires 800ma
so it means that it won't work?

Unfortunately hAP ac2 supports only 18-28V on PoE-in, so 16W of max power consumption will be more than 500mA.
However I can think of a workaround: you can feed 48V to hEX S, and then use RBGPoE as splitter + 48V to 24V DC-DC converter to power hAP ac2 by it's DC jack.

So i need to purchase 48V additional power supply to power up the hEX s and RBGPOE injector + 48v dc to dc converter. How should i connect the RBGPOE with the converter?

I guess the easiest way would be getting a couple of these: https://cdn.sparkfun.com//assets/parts/ ... 287-01.jpg
One into RBGPoE, one into hAP, and DC-DC converter in between.

Which 48v to 24v converter is recommended?

So the flow will be 48v to 24v convertor powering with the converter you mentioned earlier one comes to the hex and second to rbgpoe to power up ac2?

Which 48v to 24v converter is recommended?

No idea.
Browse aliexpress for anything capable of 30W+

So the flow will be 48v to 24v convertor powering with the converter you mentioned earlier one comes to the hex and second to rbgpoe to power up ac2?

Nope.

AC outlet --> 48V PSU --> hEX S (PoE-out) --> RBGPoE --> jack to terminal block --> 48 to 24 DC-DC converter --> terminal block to jack --> hAP ac2 (power jack)

Or you can just buy this :

https://mikrotik.com/product/rbgpoe_con_hp

Then it will be simpler:

AC outlet --> 48V PSU --> hEX S (PoE-out)--> RBGPOE-CON-HP --> hAP ac2 (PoE-in)

What if i buy RBGPOE to power up the hap ac2 with his own power supply it wont work?

What if i buy RBGPOE to power up the hap ac2 with his own power supply it wont work?

Sure it will.

Is there any distance limitation?

Is there any distance limitation?

The PSU that comes with hAP ac2 is rated 24V 0.8A (~19W).
The devices consumes 16W.

https://linktest.ru/poecalc.html

Up to 40m it should work with a good cable.
Up to 30m, I guess, you are safe with any