ZATCA has published updated e-invoicing detailed business guidelines on its website. It newly includes dedicated guidance on Advanced payments.
You can download the guidelines in English or Arabic:
English: https://zatca.gov.sa/en/E-Invoicing/Introduction/Guidelines/Documents/E-Invoicing_Detailed__Guideline.pdf
Arabic: https://zatca.gov.sa/ar/E-Invoicing/Introduction/Guidelines/Documents/E-Invoicing-Detailed-Guidelines.pdf