It's currently not possible to send receipts directly from the Payment field, which means your respondents aren't getting receipts for one-time payments made through your typeform.
To send a receipt in an email, you can set up respondent notifications, or connect your typeform to MailChimp or any other email service via Zapier to send your own receipts and emails in HTML format. Check out this Help Center article to find out how to send Gmail notifications or follow-ups from new typeform entries.
If you're comfortable with using Webhooks and APIs, you can also try this method to send receipts after accepting payments through your typeform.