Need help getting roundtrip Eurostar ticket from London to Amsterdam

That shouldn't be a problem, are you having problems with their website?

London to Amsterdam round trip for August 2025 isn't being offered yet on Eurostar website. It's probably too early to order ticket. I just wanted to be certain that I could get the ticket without having a cell phone. Thank you.

You don't need a cellphone.
What is an API?

API has something to do with English immigration. When you get Eurostar ticket, there is a form to fill out with immigration info. If you don't fill it out, you won't get ticket.

Yes, that shouldn't be a problem. Wait a few months and you should be able to buy tickets.

I’ve just looked at the Eurostar site.
API is just Advance Passenger Information.
They just want a current email address or phone number to contact you in case of changes and to issue the ticket.
Also your passport number, as you’re going from the UK to the EU.
See their Conditions of Carriage on the website, section 1:4.
You don’t have your “apply” for anything, just put the info in when booking the ticket.

That’s all.

Do you maybe mean ETA, which comes from the UK government? (I've never gotten one, yet.) You'll have one already, because you'll be in the UK. Maybe it has a number that's needed for the API form?

https://www.gov.uk/guidance/check-when-you-can-get-an-electronic-travel-authorisation-eta

Eurostar open for bookings 6 months out so are currently open to 19 July.

"Maybe it has a number that's needed for the API form?"

There's no number to enter - the Home Office collects your passport number. When carriers transmit the API data, it checks whether you have an ETA, and they get a response of either Board, No Board or Check.

Should I apply for ETA before buying Eurostar ticket for August? Thank you everyone.

The ETA is good for two years form the time it is awarded. If you plan several trips to the UK and want to maximize the number of trips you can take on one application, wait until slightly before the date you leave. If you are concerned that you might be denied, apply early so that any difficulties or rejections can be corrected.

The Eurostar website is easy to use. I generally purchase from my laptop at home (easier typing than a phone!), receive an email, and print it off. I have had instances where my train was canceled while I was in Europe. I was informed while in Europe via email. It was easy to re-schedule my train with all instructions and options made very clear.

Unless there is an unusual sale, the Eurostar prices will go up after the tickets become available and as the cheapest tickets sell out. You can take a look at various dates that are available currently and compare prices if interested in seeing price variances.

Is it correct for me to assume I should apply for ETA prior to getting Eurostar ticket? I think I have to get something similar for entry into Netherlands.

I just answered that question.

You need an ETA to enter the UK. You must get it before you arrive. You will not be stopped from purchasing a Eurostar ticket without an ETA, but will need the ETA authorization in place to enter the UK.

As of right now, there is no operating requirement for a similar electronic travel authorization for the EU. There has been a requirement for an EU ETIAS "in the works" for a number of years. It is supposed to be required in 2025, but no announcement yet of applicable date (that I am aware of) although I have seen mid-2025 mentioned. Just be aware that the new requirement is (probably) on the way and keep watch for dates, requirements, and application procedures.

Thank you so very much for your information. I really appreciate it.

I think I have to get something similar for entry into Netherlands.

Maybe.

Depends what your citizenship is.