Requirement for credentials doesn't match PayPal sandbox

These Fields:

• API Username
• API Password
• Signature

Are for PayPal's newer Express Checkout system (NVP/SOAP API). To get this module working you have to use a credentials screen that no longer exist in the new PayPal UI.

The instructions for getting the credentials you need are here:
https://developer.paypal.com/api/nvp-soap/apiCredentials/#api-signatures
... however the instructions only make sense on the old site, which you can still get to by going here: https://history.paypal.com/cgi-bin/webscr?cmd=_history

Once you’re there, click the gear:

You'll end up here: https://www.paypal.com/businessmanage/profile/loginSecurity

Pulldown "Account Settings":

You'll end up here: https://www.paypal.com/businessmanage/account/accountAccess

... where you'll find the "API Access » Update" link that doesn’t exist on the new site:

Clicking that will plop you out here: https://www.paypal.com/businessmanage/credentials/apiaccess
... where another link that doesn’t exist on the new site can be found:

... where at long last you'll find the info you need:

... to add this commerce payment gateway on your site: example.com/admin/commerce/config/payment-gateways/add

Good luck!

@perfectcu.be wonderful support, thank you. I no longer need this module as my customer looked for a different solution (I had this issue 2 years ago). Now working mainly with BackdropCMS, so might revisit this, with your help.