Trying to update authorize.net payment portal on a WordPress site

[emriver]

We recently changed our payment processor and have not been able to get our authorize.net payment portal to work with the new processor. We have a very simple authorize.net integration on our site, which is just a 'Pay Now' button which links to a payment page from authorize.net. The code that we have on our site is the following:

<form name="PrePage" method = "post" action = "https://Simplecheckout.authorize.net/payment/CatalogPayment.aspx">
<input type = "hidden" name = "LinkId" value="f21f8339-d405-43de-bf00-8f04aa622e92" />
<button type="submit" style="cursor: pointer;">Pay Now</button>
</form>

This piece of code was given to us by our previous payment processor and was functioning without issue. However, our new payment processor has not given us any upated code, simply a new API login ID and transaction key. How can we generate an updated piece of code from the ID and key?

You can view our payment page here:

https://emriver.com/make-a-payment/

[emriver]

Update: I've found the place where I can generate a new button code in Tools > Simple Checkout.

However, when creating a new button item it requires that I enter a price. How can I generate a button that does not include a price?

[emriver · Accepted solution]

Update: I had to change the transaction type to 'donation'