Can you: Yes.

Should you: Probably not.

ACP charge a hefty fee, unless you can’t get your reservations elsewhere then they are best avoided.

Which countries are you looking to get reservations for?

Thanks so much for helping me negotiate the labyrinth! 
UK at this point. We dropped the ball on scheduling for France and Netherlands. Alas. 

Some experienced travellers have made a guide on how to make reservations. You can look at the guide in the link:

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105

If you, after having looked at the guide, have questions about how to make specific reservation, please give your travel details (departure date, time and route) preferably in a new post, and you will get advice. 

 The short answer is that you do not need reservations for trains in Britain, the only exceptions to this are Eurostar trains to/from London via Channel Tunnel and sleeper trains in Britain.

Heathrow Express is also an exception in that Eurail passes are not valid, happily there are frequent alternative (but a little slower) Elizabeth Line trains that are valid.

All other trains in Britian do not require reservations or are unreservable. British trains always have been (with the exception of some now removed COVID nonsense) primarily walk-up. Standard fares are not train specific and using them without reservations is not unusual at all. Even now many people use non-assigned tickets without reservations and many of the main long-distance routes have whole carriages or sections that are unreserved.

The Eurail app says some trains require reservations, this is incorrect.

ACP charge a ridiculous fee for reservations, if you want reservations they can be obtained for free at any British rail station with a staffed ticket counter or also for free online from GWR.com (one of the rail operators whose booking system allows issuing reservations without a ticket)

Got problem with reservation on ACPs website, anyone more?

As advised, don't do reservations there.

You'll pay for free reservations.

For trains in the UK, use gwr.com. See advice here : 

https://community.eurail.com/train-connections-reservations-47/how-to-get-reservations-105?postid=11554#post11554

For other countries let us know the route, date and departure time

But If I want to...please ask my question insted

Why would you pay for free reservations ? There's not a single advantage. ACP won't let you know in case of delays or strikes for example.

The reservations can be done elsewhere, I'm not saying that you shouldn't make them.

(In the UK they're all optional but can be done on busy mainlines)

I just asked if anyone had problem with their website, so could you answer my question or keep on being rude...

ACP can do more reservations than just for the UK but they typically add a higher booking fee than any other website, so I don't recommend them and I don't use them. Maybe if you have a voucher from them, that could be a reason to book through them.

Now as to your problem:

"Got a problem” is really, really vague. What problem? At which step does it appear and what train are you trying to book?