Context: [AlphaCommerceHub] How does «Show Merchant Details» work for a pay page?
I have found the solution.
You can setup these fields contents on the pay page form in the «General Information» section:
The payment form’s «Pay To» field shows the contents of the «Merchant Pay To» pay page’s field.
The payment form’s «Customer Enquiries» field shows the contents of the «Merchant Contact» pay page’s field: