For what it's worth:

I went to my bank to get a new debit card, and at the same time mentioned that last year my credit card would not work in dispensing machines, such as getting metro tickets. On the other hand, my debit card did work a few years ago in similar machines in Amsterdam. I was told that the pin number on the American chip credit card (issued by my credit union) is only for withdrawing cash from an ATM; for other transactions requiring a pin, I should use my debit card.

Yes, that is correct. You need to get a chip and PIN credit card that supports purchases with the PIN if you don't want to use your debit card, at certain machines (I usually avoid making purchases with my debit card). It's easy for most people to get an Andrews Federal Credit Union Visa (no annual fee, no currency conversion fee) if you want a credit card that works at all machines. I used to have one until my credit union switched to a true chip and PIN credit card. To join Andrews (don't need to go into a physical branch - they are in Maryland), all you need to do is join the American Consumer Council (ACC) for $5 for one year and then you can join the credit union. (Credit unions sometimes have weird rules about who is eligible to join.)

That said, I've rarely needed a chip and PIN credit card in Europe anyway. Even my chip and signature card (usually one with better rewards than chip and PIN card) works at most machines in Europe, even for bus or train tickets. There are exceptions. I could not use my BofA chip signature card last year at train machines in Italy and France, though some people have claimed success with other chip and signature cards at those machines. I'm pretty sure one still can't buy train tickets at the Netherlands train ticket machines without a chip and PIN card (or cash) - my chip and signature credit cards have never worked there.

Thanks, Michael. As Andrew suggests, if you need a true chip and PIN card, consider Andres Federal Credit Union; I have one from them, and I also have one from the United National Federal Credit Union. As I understand it, most cards issued in the US are chip with a PIN that can be used at ATMs, but not to authorize purchases when a PIN is required for that purpose.

Interesting question

I discussed the issue with a shop keeper and he now finds that people in Europe are begining to forget their PINs as they "touchless" technology, so by the time the USA catch up with PINs Europe will have moved on.

It's true. All you have to do these days here in most shops is hold your card over the machine and the sale registers instantly.

Here you can only use contactless for payments up to €25, with a debit card, above that you need a Pin.
So few shops here accept a credit card I have a struggle to remember my Pin when I do use it. No idea if you can use it contactless.
My sons pay for everything with their phones, using NFC. I prefer to use my card, being an old fogey.

I don't know where you bought metro tickets, but I've been able to use my American CC in ticket machines in France at rail stations and metro stations, I think, without a problem (I know I've used it in rail stations), and it doesn't have a PIN (except for ATMs, of course, which has been around years and years). What I am very surprised at is the remark that you could use your debit card in such machines, but not credit cards. I thought American debit card PINs were the same way as credit cards, nothing special, you can use them in ATM machines but that's all. I don't own a debit card so never tried it, though.

" I was told that the pin number on the American chip credit card (issued by my credit union) is only for withdrawing cash from an ATM; for other transactions requiring a pin, I should use my debit card."

For what it's worth, what you were told is either correct for your specific card, or complete crap if used as a general rule.

This is issuer-dependent and the US has so many issuers that over-generalizations are more OVER than accurate. My Barclays card, issued by Barclays US, worked as a chip and pin three years ago in a country known for its innumerable Shinto shrines, but operates as a chip/sign in the US.

I have a VISA credit card, chip and pin, from USAA that I used successfully at metro ticket machines in Paris as well as fuel pumps in small towns in the countryside. The only place it didn't work was at a self service kiosk at McDonalds. I had to take my receipt to the attended register to complete the transaction.

A follow up with our actual experience. Our pin card was accepted at all unattended stations (metro tickets, gasoline stations, toll booths). For a short moment it can be confusing because a request appears on the screen for the pin number, but before I had time to enter it, the machine would process the card. There was no minimum as the tolls would sometimes amount to less than a euro.

I just got back from France and had no problem whatsoever using my American credit card (chip and signature only) in all train station machines or the Paris metro ticket machines.

FWIW, during my 2016 trip to Paris and Bordeaux, I used my Capital One chip & signature card in the unmanned ticket machines in the Bordeaux train station, and the ticket dispenser in the Montparnasse Gare. I also used it in restaurants but had to sign.

To be safe, avoid unmanned gas stations! Although I'm seeing Michael was OK.

Here's the other thing: not every chip and signature card is the same, either. Last year in Italy, I could not use the big bank chip and signature credit card in the train ticket machines in either Italy or France - I had to use my chip and PIN card. But others have reported no problems with their chip and signature cards in those machines. So...don't COUNT on being able to use your chip and signature cards in those machines, but they MIGHT work. Mine didn't.