Embeddable Payment Form Separate from E Commerce

Hi there, I am looking for options to have an embeddable form to accept simple payments on a squarespace page. It would:

• Not be a part of an e-commerce page
• Would require the payment to be flexible (i.e., the user can input the value)
• Would not be a donation
• Would need some simple information fields (name, address, invoice #, etc)
• Would allow the user to pay via credit card and integrate with common payment processors

Is anyone aware of any third party services that play well with squarespace that would work for this use case?

Thank you so much!