I found this: https://www.paypal.com/uk/smarthelp/article/why-did-i-get-api-error-code-10525-ts1441 It has this as the cause:

In a Direct Payment API call, the transaction has a zero value passed in as a parameter.

The solution:

Review your API call to ensure a value or $0.01 or more is being submitted in your API call.

Does this mean the PayPal integration will never work with zero value orders? I guess it makes sense, I just never noticed it before and the error message is slightly misleading because the description says it’s below zero

I mean it makes sense. There's no need for a payment gateway/provider like PayPal to process anything in the transaction. I would assume that if the payment due is 0, SCA would just skip the whole thing and just place the order 🤔

I’m pretty sure it’s a configuration setting to stop it trying to process if the value is 0? This site definitely doesn’t have it enabled though so I’d probably have to run it past some people and then test it

There is a setting in the web site record to hide the payment page if the order equals zero: "HIDE PAYMENT PAGE IF ORDER TOTAL EQUALS ZERO"

Thanks Flo that’s the option I was thinking of!